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 (this.pdfDocument) {
      this.eventBus.dispatch("pagesdestroy", { source: this });
      this._cancelRendering();
      this._resetView();
      if (this.findController) {
        this.findController.setDocument(null);
      }
      if (this._scriptingManager) {
        this._scriptingManager.setDocument(null);
      }
    }
    this.pdfDocument = pdfDocument;
    if (!pdfDocument) {
      return;
    }
    const isPureXfa = pdfDocument.isPureXfa;
    const pagesCount = pdfDocument.numPages;
    const firstPagePromise = pdfDocument.getPage(1);
    
    const optionalContentConfigPromise = pdfDocument.getOptionalContentConfig();
    this._pagesCapability.promise.then(() => {
      this.eventBus.dispatch("pagesloaded", {
        source: this,
        pagesCount,
      });
    });
    this._onBeforeDraw = evt => {
      const pageView = this._pages[evt.pageNumber - 1];
      if (!pageView) {
        return;