schuyler · Daria-E · Aug 15, 2026 · Aug 19, 2026 · Aug 19, 2026
diff --git a/MacDown 3000.xcodeproj/project.pbxproj b/MacDown 3000.xcodeproj/project.pbxproj
@@ -155,6 +155,7 @@
 		ISSUE313TOOLBARBUILDFILE /* MPToolbarControllerTests.m in Sources */ = {isa = PBXBuildFile; fileRef = ISSUE313TOOLBARFILEREF /* MPToolbarControllerTests.m */; };
 		ISSUE318STYLERELBUILDFILE /* MPDocumentStyleUpdateTests.m in Sources */ = {isa = PBXBuildFile; fileRef = ISSUE318STYLERELFILEREF /* MPDocumentStyleUpdateTests.m */; };
 		ISSUE325MJSCRLBUILDFILE /* MPMathJaxScrollTests.m in Sources */ = {isa = PBXBuildFile; fileRef = ISSUE325MJSCRLFILEREF /* MPMathJaxScrollTests.m */; };
+		MJLOCALFONTSBUILDFILE /* MPMathJaxLocalFontsTests.m in Sources */ = {isa = PBXBuildFile; fileRef = MJLOCALFONTSFILEREF /* MPMathJaxLocalFontsTests.m */; };
 		ISSUE331MRMDRNDRBUILDFILE /* MPMermaidRenderingTests.m in Sources */ = {isa = PBXBuildFile; fileRef = ISSUE331MRMDRNDRFILEREF /* MPMermaidRenderingTests.m */; };
 		ISSUE332GVIZRNDRBUILDFILE /* MPGraphvizRenderingTests.m in Sources */ = {isa = PBXBuildFile; fileRef = ISSUE332GVIZRNDRFILEREF /* MPGraphvizRenderingTests.m */; };
 		ISSUE341IMGRENDERBUILDFILE /* MPImageRenderingTests.m in Sources */ = {isa = PBXBuildFile; fileRef = ISSUE341IMGRENDERFILEREF /* MPImageRenderingTests.m */; };
@@ -732,6 +733,7 @@
 		ISSUE313TOOLBARFILEREF /* MPToolbarControllerTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MPToolbarControllerTests.m; sourceTree = "<group>"; };
 		ISSUE318STYLERELFILEREF /* MPDocumentStyleUpdateTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MPDocumentStyleUpdateTests.m; sourceTree = "<group>"; };
 		ISSUE325MJSCRLFILEREF /* MPMathJaxScrollTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MPMathJaxScrollTests.m; sourceTree = "<group>"; };
+		MJLOCALFONTSFILEREF /* MPMathJaxLocalFontsTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MPMathJaxLocalFontsTests.m; sourceTree = "<group>"; };
 		ISSUE331MRMDRNDRFILEREF /* MPMermaidRenderingTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MPMermaidRenderingTests.m; sourceTree = "<group>"; };
 		ISSUE332GVIZRNDRFILEREF /* MPGraphvizRenderingTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MPGraphvizRenderingTests.m; sourceTree = "<group>"; };
 		ISSUE341IMGRENDERFILEREF /* MPImageRenderingTests.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = MPImageRenderingTests.m; sourceTree = "<group>"; };
@@ -1175,6 +1177,7 @@
 				8552820CEE8D00E83AEE3897 /* MPHTMLResourceURLsTests.m */,
 				ISSUE341IMGRENDERFILEREF /* MPImageRenderingTests.m */,
 				ISSUE325MJSCRLFILEREF /* MPMathJaxScrollTests.m */,
+				MJLOCALFONTSFILEREF /* MPMathJaxLocalFontsTests.m */,
 				1FCDCA371944F97800B1F966 /* Supporting Files */,
 				B3BD139B59E787FBB9F38228 /* MPEditorViewSubstitutionTests.m */,
 				66A67CD2B90882C7F91B6251 /* MPEditorViewPasteboardTests.m */,
@@ -1929,6 +1932,7 @@
 				ISSUE278TABLEBUILDFILE /* MPInsertTableTests.m in Sources */,
 				ISSUE543EXTCHGBUILDFILE /* MPExternalChangeReloadTests.m in Sources */,
 				ISSUE325MJSCRLBUILDFILE /* MPMathJaxScrollTests.m in Sources */,
+				MJLOCALFONTSBUILDFILE /* MPMathJaxLocalFontsTests.m in Sources */,
 				5AD88BF0766B938F9D61A831 /* MPEditorViewSubstitutionTests.m in Sources */,
 				C185BB0F201C78DF6D946E1F /* MPEditorViewPasteboardTests.m in Sources */,
 				ISSUE313TOOLBARBUILDFILE /* MPToolbarControllerTests.m in Sources */,

diff --git a/MacDown/Code/Document/MPDocument.m b/MacDown/Code/Document/MPDocument.m
@@ -1792,14 +1792,46 @@ - (BOOL)textViewShouldMoveToLeftEndOfLine:(NSTextView *)textView
 
 - (NSURLRequest *)webView:(WebView *)sender resource:(id)identifier willSendRequest:(NSURLRequest *)request redirectResponse:(NSURLResponse *)redirectResponse fromDataSource:(WebDataSource *)dataSource
 {
-
+    // The MathJax loader is served from the bundle, carrying its "?config=…"
+    // query so MathJax still loads the right combined config.
     if ([[request.URL lastPathComponent] isEqualToString:@"MathJax.js"])
     {
         NSURLComponents *origComps = [NSURLComponents componentsWithURL:[request URL] resolvingAgainstBaseURL:YES];
         NSURLComponents *updatedComps = [NSURLComponents componentsWithURL:[[NSBundle mainBundle] URLForResource:@"MathJax" withExtension:@"js" subdirectory:@"MathJax"] resolvingAgainstBaseURL:NO];
         [updatedComps setQueryItems:[origComps queryItems]];
 
-        request = [NSURLRequest requestWithURL:[updatedComps URL]];
+        return [NSURLRequest requestWithURL:[updatedComps URL]];
+    }
+
+    // The TeX HTML-CSS web fonts also ship in the bundle. Serve them locally too:
+    // without the fonts local, the HTML-CSS output jax waits on a render-time
+    // web-font fetch and, when it times out, falls back to bitmap image fonts
+    // that pixelate on zoom. Any MathJax CDN resource whose path maps to a file
+    // present in the bundle is redirected; the rest (config, jax.js, fontdata.js)
+    // fall through to the CDN unchanged, so this only ever short-circuits a load
+    // to a file that exists. The "?V=…" query is dropped — a file: URL with a
+    // query may not resolve, which would fail the load back into the fallback.
+    NSURL *cdn = [NSURL URLWithString:kMPMathJaxCDN];
+    NSURL *url = request.URL;
+    if (cdn.host.length && [url.host isEqualToString:cdn.host])
+    {
+        // Directory on the CDN that holds MathJax.js, e.g.
+        // "/ajax/libs/mathjax/2.7.3/". The trailing slash keeps a sibling
+        // version directory (…/2.7.30/) from matching this one's prefix.
+        NSString *prefix = [[cdn.path stringByDeletingLastPathComponent]
+                            stringByAppendingString:@"/"];
+        if ([url.path hasPrefix:prefix])
+        {
+            NSString *subpath = [url.path substringFromIndex:prefix.length];
+            NSURL *mathJaxDir =
+                [[NSBundle mainBundle].resourceURL URLByAppendingPathComponent:@"MathJax"];
+            NSURL *local = [mathJaxDir URLByAppendingPathComponent:subpath];
+            if (subpath.length &&
+                [[NSFileManager defaultManager] fileExistsAtPath:local.path])
+            {
+                request = [NSURLRequest requestWithURL:local];
+            }
+        }
     }
 
     return request;

diff --git a/MacDown/Code/Document/MPRenderer.h b/MacDown/Code/Document/MPRenderer.h
@@ -10,6 +10,11 @@
 @protocol MPRendererDataSource;
 @protocol MPRendererDelegate;
 
+// The MathJax loader URL the preview requests. The bundle serves this and the
+// TeX fonts locally (see -[MPDocument webView:resource:willSendRequest:…]), so
+// MPDocument matches requests against this origin.
+extern NSString * const kMPMathJaxCDN;
+
 
 typedef NS_ENUM(NSUInteger, MPCodeBlockAccessoryType)
 {

diff --git a/MacDown/Code/Document/MPRenderer.m b/MacDown/Code/Document/MPRenderer.m
@@ -23,7 +23,7 @@
 // of https://github.com/mathjax/MathJax/issues/548. If the fix has been merged
 // in to MathJax, then the WebResourceLoadDelegate can be removed from MPDocument
 // and MathJax.js can be removed from this project.
-static NSString * const kMPMathJaxCDN =
+NSString * const kMPMathJaxCDN =
     @"https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.3/MathJax.js"
     @"?config=TeX-AMS-MML_HTMLorMML";
 static NSString * const kMPPrismScriptDirectory = @"Prism/components";
@@ -486,6 +486,28 @@ NS_INLINE void MPFreeHTMLRenderer(hoedown_renderer *htmlRenderer)
     return escaped;
 }
 
+/**
+ * Origin of kMPMathJaxCDN as a CSP source expression, e.g.
+ * "https://cdnjs.cloudflare.com".
+ *
+ * MathJax resolves its configuration, jax and fonts against the script
+ * element's own src, so every one of them comes from this origin. Deriving the
+ * source expression from the URL keeps the policy from drifting away from the
+ * URL actually loaded when the CDN changes.
+ */
+NS_INLINE NSString *MPMathJaxCDNOrigin(void)
+{
+    NSURLComponents *cdn = [NSURLComponents componentsWithString:kMPMathJaxCDN];
+    NSCAssert(cdn.scheme.length && cdn.host.length,
+              @"kMPMathJaxCDN must carry a scheme and host");
+    if (cdn.port)
+    {
+        return [NSString stringWithFormat:@"%@://%@:%@",
+                                          cdn.scheme, cdn.host, cdn.port];
+    }
+    return [NSString stringWithFormat:@"%@://%@", cdn.scheme, cdn.host];
+}
+
 NS_INLINE NSString *MPPreviewContentSecurityPolicy(void)
 {
     // MathJax 2.x relies on eval/new Function during startup, and bundled
@@ -496,17 +518,24 @@ NS_INLINE void MPFreeHTMLRenderer(hoedown_renderer *htmlRenderer)
     // that source — the <img> container still lays out, but the bits never
     // load. MPImageRenderingTests pins this contract; update it deliberately
     // if you tighten the policy.
-    return @"default-src 'none'; "
-           @"base-uri 'none'; "
-           @"form-action 'none'; "
-           @"object-src 'none'; "
-           @"frame-src 'none'; "
-           @"img-src data: file: http: https:; "
-           @"media-src data: file: http: https:; "
-           @"style-src 'self' 'unsafe-inline' file:; "
-           @"font-src data: file:; "
-           @"connect-src http: https:; "
-           @"script-src 'self' file: https://cdnjs.cloudflare.com 'unsafe-eval'";
+    //
+    // font-src carries the MathJax origin for the same reason script-src does:
+    // the TeX faces are fetched from it, and blocking them makes the HTML-CSS
+    // output jax stall for its web-font timeout and then fall back to bitmap
+    // image fonts.
+    NSString *mathJax = MPMathJaxCDNOrigin();
+    return [NSString stringWithFormat:
+            @"default-src 'none'; "
+            @"base-uri 'none'; "
+            @"form-action 'none'; "
+            @"object-src 'none'; "
+            @"frame-src 'none'; "
+            @"img-src data: file: http: https:; "
+            @"media-src data: file: http: https:; "
+            @"style-src 'self' 'unsafe-inline' file:; "
+            @"font-src data: file: %@; "
+            @"connect-src http: https:; "
+            @"script-src 'self' file: %@ 'unsafe-eval'", mathJax, mathJax];
 }
 
 NS_INLINE NSString *MPPreviewHeadTags(NSString *checkboxBridgeToken)

diff --git a/MacDown/Resources/MathJax/init.js b/MacDown/Resources/MathJax/init.js
@@ -2,7 +2,24 @@
 
 MathJax.Hub.Config({
 	'showProcessingMessages': false,
-	'messageStyle': 'none'
+	'messageStyle': 'none',
+
+	// The HTML-CSS output jax prefers fonts installed on the machine over
+	// MathJax's own, and its default availableFonts list names STIX. macOS
+	// ships STIX 1.x as system-reserved faces that WebKit resolves by name, so
+	// the preview picks them up and typesets digits and operators in
+	// STIXGeneral-Regular — a Times-metric face indistinguishable from body
+	// text. Browsers that do not enumerate those faces, such as Firefox, load
+	// MathJax's TeX fonts instead and render the same document correctly.
+	//
+	// Emptying the list makes the preview do the same. preferredFont is nulled
+	// alongside it because MathJax tests the preferred font even when it is
+	// absent from availableFonts, so the list alone would still take the local
+	// path on a machine carrying MathJax's own TeX fonts.
+	'HTML-CSS': {
+		'availableFonts': [],
+		'preferredFont': null
+	}
 });
 
 if (typeof MathJaxListener !== 'undefined') {

diff --git a/MacDownTests/MPMathJaxLocalFontsTests.m b/MacDownTests/MPMathJaxLocalFontsTests.m
@@ -0,0 +1,150 @@
+//
+//  MPMathJaxLocalFontsTests.m
+//  MacDown 3000
+//
+//  MathJax's HTML-CSS output jax renders in vector web fonts, but when those
+//  fonts are fetched from the CDN at render time and the fetch times out it
+//  falls back to bitmap image fonts that pixelate on zoom. The app bundles the
+//  TeX woff fonts and the resource-load delegate serves them (and the MathJax
+//  loader) from the bundle. These tests pin that redirect and the bundled set.
+//
+
+#import <XCTest/XCTest.h>
+#import <WebKit/WebKit.h>
+#import "MPDocument.h"
+
+// The WebResourceLoadDelegate method under test (implemented in MPDocument.m).
+@interface MPDocument (LocalFontsTesting)
+- (NSURLRequest *)webView:(WebView *)sender resource:(id)identifier
+          willSendRequest:(NSURLRequest *)request
+         redirectResponse:(NSURLResponse *)redirectResponse
+           fromDataSource:(WebDataSource *)dataSource;
+@end
+
+// Must match kMPMathJaxCDN's origin and version directory in MPRenderer.m.
+static NSString * const kMPTestCDNBase =
+    @"https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.3/";
+
+
+@interface MPMathJaxLocalFontsTests : XCTestCase
+@property (strong) MPDocument *document;
+@end
+
+
+@implementation MPMathJaxLocalFontsTests
+
+- (void)setUp
+{
+    [super setUp];
+    self.document = [[MPDocument alloc] init];
+}
+
+- (void)tearDown
+{
+    self.document = nil;
+    [super tearDown];
+}
+
+/// Runs a CDN request (base + suffix) through the real delegate and returns the
+/// URL it decides to load.
+- (NSURL *)resolvedURLForSuffix:(NSString *)suffix
+{
+    NSURL *url = [NSURL URLWithString:
+                  [kMPTestCDNBase stringByAppendingString:suffix]];
+    NSURLRequest *req = [NSURLRequest requestWithURL:url];
+    NSURLRequest *out = [self.document webView:nil resource:nil
+                               willSendRequest:req redirectResponse:nil
+                                fromDataSource:nil];
+    return out.URL;
+}
+
+- (void)testWoffFontRedirectsToBundleWithoutQuery
+{
+    NSURL *result = [self resolvedURLForSuffix:
+        @"fonts/HTML-CSS/TeX/woff/MathJax_Main-Regular.woff?V=2.7.3"];
+
+    XCTAssertTrue(result.isFileURL,
+                  @"A bundled woff font should be served from the bundle");
+    XCTAssertNil(result.query,
+                 @"The local font URL must carry no query, or file: may not "
+                 @"resolve and the load falls back to image fonts");
+    XCTAssertTrue([result.path hasSuffix:
+        @"/MathJax/fonts/HTML-CSS/TeX/woff/MathJax_Main-Regular.woff"],
+        @"Should map to the bundled font path, got %@", result.path);
+    XCTAssertTrue([[NSFileManager defaultManager] fileExistsAtPath:result.path],
+                  @"The redirected font must actually exist in the bundle");
+}
+
+- (void)testUnbundledResourcePassesThroughToCDN
+{
+    // jax.js is not bundled, so the delegate must leave the request on the CDN.
+    NSURL *result = [self resolvedURLForSuffix:
+        @"jax/output/HTML-CSS/jax.js?V=2.7.3"];
+
+    XCTAssertFalse(result.isFileURL,
+                   @"An un-bundled resource must not be redirected locally");
+    XCTAssertEqualObjects(result.host, @"cdnjs.cloudflare.com");
+    XCTAssertTrue([result.path hasSuffix:@"jax/output/HTML-CSS/jax.js"]);
+}
+
+- (void)testMathJaxLoaderStillRedirectsWithConfigQuery
+{
+    // Regression guard for the behaviour the generalised redirect replaces.
+    NSURL *result = [self resolvedURLForSuffix:
+        @"MathJax.js?config=TeX-AMS-MML_HTMLorMML"];
+
+    XCTAssertTrue(result.isFileURL,
+                  @"MathJax.js should be served from the bundle");
+    XCTAssertTrue([result.path hasSuffix:@"/MathJax/MathJax.js"],
+                  @"Should map to the bundled loader, got %@", result.path);
+    XCTAssertEqualObjects(result.query, @"config=TeX-AMS-MML_HTMLorMML",
+                          @"MathJax.js must keep its config query");
+}
+
+- (void)testFullTeXWoffSetIsBundled
+{
+    // Authoritative list of the MathJax 2.7.3 HTML-CSS TeX woff files, copied
+    // from the upstream distribution. It is intentionally NOT enumerated from
+    // the bundle's own contents: a list read back from what was dropped could
+    // never fail on an incomplete drop. A missing family (e.g. AMS) would let a
+    // document's glyphs fetch remotely and pixelate on a timeout.
+    NSArray<NSString *> *expected = @[
+        @"MathJax_AMS-Regular",
+        @"MathJax_Caligraphic-Bold",
+        @"MathJax_Caligraphic-Regular",
+        @"MathJax_Fraktur-Bold",
+        @"MathJax_Fraktur-Regular",
+        @"MathJax_Main-Bold",
+        @"MathJax_Main-Italic",
+        @"MathJax_Main-Regular",
+        @"MathJax_Math-BoldItalic",
+        @"MathJax_Math-Italic",
+        @"MathJax_Math-Regular",
+        @"MathJax_SansSerif-Bold",
+        @"MathJax_SansSerif-Italic",
+        @"MathJax_SansSerif-Regular",
+        @"MathJax_Script-Regular",
+        @"MathJax_Size1-Regular",
+        @"MathJax_Size2-Regular",
+        @"MathJax_Size3-Regular",
+        @"MathJax_Size4-Regular",
+        @"MathJax_Typewriter-Regular",
+        @"MathJax_Vector-Bold",
+        @"MathJax_Vector-Regular",
+    ];
+
+    NSURL *woffDir = [[NSBundle mainBundle].resourceURL
+        URLByAppendingPathComponent:@"MathJax/fonts/HTML-CSS/TeX/woff"];
+
+    for (NSString *name in expected)
+    {
+        NSURL *font = [woffDir URLByAppendingPathComponent:
+                       [name stringByAppendingPathExtension:@"woff"]];
+        XCTAssertTrue([[NSFileManager defaultManager] fileExistsAtPath:font.path],
+                      @"missing bundled TeX font: %@.woff", name);
+    }
+    XCTAssertEqual(expected.count, 22u,
+                   @"The 2.7.3 TeX woff set has 22 files");
+}
+
+@end