Fix pinch-to-zoom on mac for the Firefox builtin viewer

In the mac case we don't want to care about the scaleFactor threshold
because else if too big another move could start and then subsequent
events aren't considered as wheel events.
It isn't really ideal and at some point we'll need to find a way at
least for the Firefox case to get the real events instead of the fake
wheel ones.

src/pdf.js

@@ -32,6 +32,7 @@ import {
   CMapCompressionType,
   createPromiseCapability,
   createValidAbsoluteUrl,
+  FeatureTest,
   InvalidPDFException,
   MissingPDFException,
   OPS,
@@ -89,6 +90,7 @@ export {
   CMapCompressionType,
   createPromiseCapability,
   createValidAbsoluteUrl,
+  FeatureTest,
   getDocument,
   getFilenameFromUrl,
   getPdfFilenameFromUrl,

web/app.js

@@ -38,6 +38,7 @@ import {
   AnnotationEditorType,
   build,
   createPromiseCapability,
+  FeatureTest,
   getDocument,
   getFilenameFromUrl,
   getPdfFilenameFromUrl,
@@ -2695,12 +2696,16 @@ function webViewerWheel(evt) {
   // https://searchfox.org/mozilla-central/rev/d62c4c4d5547064487006a1506287da394b64724/widget/InputData.cpp#618-626
   let scaleFactor = Math.exp(-evt.deltaY / 100);
 
+  const isBuiltInMac =
+    typeof PDFJSDev !== "undefined" &&
+    PDFJSDev.test("MOZCENTRAL") &&
+    FeatureTest.platform.isMac;
   const isPinchToZoom =
     evt.ctrlKey &&
     !PDFViewerApplication._isCtrlKeyDown &&
     deltaMode === WheelEvent.DOM_DELTA_PIXEL &&
     evt.deltaX === 0 &&
-    Math.abs(scaleFactor - 1) < 0.05 &&
+    (Math.abs(scaleFactor - 1) < 0.05 || isBuiltInMac) &&
     evt.deltaZ === 0;
 
   if (