Add another preference check to detect if web fonts are disabled in Firefox

extensions/firefox/components/PdfStreamConverter.js

@@ -376,8 +376,9 @@ ChromeActions.prototype = {
            'updateControlState' in getChromeWindow(this.domWindow).gFindBar;
   },
   supportsDocumentFonts: function() {
-    var pref = getIntPref('browser.display.use_document_fonts', 1);
-    return !!pref;
+    var prefBrowser = getIntPref('browser.display.use_document_fonts', 1);
+    var prefGfx = getBoolPref('gfx.downloadable_fonts.enabled', true);
+    return (!!prefBrowser && prefGfx);
   },
   fallback: function(url, sendResponse) {
     var self = this;