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)

this.pdfOutlineViewer = new PDFOutlineViewer({
      container: appConfig.sidebar.outlineView,
      eventBus,
      linkService: pdfLinkService,
    });
    this.pdfAttachmentViewer = new PDFAttachmentViewer({
      container: appConfig.sidebar.attachmentsView,
      eventBus,
      downloadManager,
    });
    this.pdfLayerViewer = new PDFLayerViewer({
      container: appConfig.sidebar.layersView,
      eventBus,
      l10n: this.l10n,
    });
    this.pdfSidebar = new PDFSidebar({
      elements: appConfig.sidebar,
      pdfViewer: this.pdfViewer,
      pdfThumbnailViewer: this.pdfThumbnailViewer,
      eventBus,
      l10n: this.l10n,
    });
    this.pdfSidebar.onToggled = this.forceRendering.bind(this);
    this.pdfSidebarResizer = new PDFSidebarResizer(
      appConfig.sidebarResizer,
      eventBus,
      this.l10n
    );
  },
  run(config) {