fix COLR font check being racy

also make sure it doesn't run more than once.
keeping the FF sniffing because missing "extract canvas data" permissions
would still break the check.

src/utils/FontManager.js

@@ -21,21 +21,16 @@ limitations under the License.
  * MIT license
  */
 
-let colrFontSupported = undefined;
-
 async function isColrFontSupported() {
-    if (colrFontSupported !== undefined) {
-        return colrFontSupported;
-    }
-
     console.log("Checking for COLR support");
 
     // Firefox has supported COLR fonts since version 26
-    // but doesn't support the check below with content blocking enabled.
+    // but doesn't support the check below without
+    // "Extract canvas data" permissions
+    // when content blocking is enabled.
     if (navigator.userAgent.includes("Firefox")) {
-        colrFontSupported = true;
         console.log("Browser is Firefox - assuming COLR is supported");
-        return colrFontSupported;
+        return true;
     }
 
     try {
@@ -61,26 +56,25 @@ async function isColrFontSupported() {
 
         img.src = 'data:image/svg+xml;charset=utf-8,' + encodeURIComponent(svg);
 
-        // FIXME wait for safari load our colr font
-        const wait = ms => new Promise((r, j)=>setTimeout(r, ms));
-        await wait(500);
-
+        console.log("Waiting for COLR SVG to load");
+        await new Promise(resolve => img.onload = resolve);
         console.log("Drawing canvas to detect COLR support");
         context.drawImage(img, 0, 0);
-        colrFontSupported = (context.getImageData(10, 10, 1, 1).data[0] === 200);
+        const colrFontSupported = (context.getImageData(10, 10, 1, 1).data[0] === 200);
         console.log("Canvas check revealed COLR is supported? " + colrFontSupported);
+        return colrFontSupported;
     } catch (e) {
         console.error("Couldn't load COLR font", e);
-        colrFontSupported = false;
+        return false;
     }
-
-    return colrFontSupported;
 }
 
+let colrFontCheckStarted = false;
 export async function fixupColorFonts() {
-    if (colrFontSupported !== undefined) {
+    if (colrFontCheckStarted) {
         return;
     }
+    colrFontCheckStarted = true;
 
     if (await isColrFontSupported()) {
         const path = `url('${require("../../res/fonts/Twemoji_Mozilla/TwemojiMozilla-colr.woff2")}')`;