I was wondering if WebGL is considered stable enough to be enabled by default. It makes some PDFs render much faster and it has been off by default for a while now, so we have had quite some time to test it.

If we decide to enable WebGL by default, we should not forget to update https://github.com/mozilla/pdf.js/blob/master/extensions/chromium/preferences_schema.json#L39 as well.

/cc @yurydelendik 
/cc @Snuffleupagus (because IIRC you were testing WebGL too)

if (document.blockUnblockOnload) {
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    this._unblockDocumentLoadEvent = () => {};
  },
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};
let validateFileURL;
if (typeof PDFJSDev === "undefined" || PDFJSDev.test("GENERIC")) {
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