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)

storedHash,
    { rotation, sidebarView, scrollMode, spreadMode } = {}
  ) {
    const setRotation = angle => {
      if (isValidRotation(angle)) {
        this.pdfViewer.pagesRotation = angle;
      }
    };
    const setViewerModes = (scroll, spread) => {
      if (isValidScrollMode(scroll)) {
        this.pdfViewer.scrollMode = scroll;
      }
      if (isValidSpreadMode(spread)) {
        this.pdfViewer.spreadMode = spread;
      }
    };
    this.isInitialViewSet = true;
    this.pdfSidebar.setInitialView(sidebarView);
    setViewerModes(scrollMode, spreadMode);
    if (this.initialBookmark) {
      setRotation(this.initialRotation);
      delete this.initialRotation;
      this.pdfLinkService.setHash(this.initialBookmark);
      this.initialBookmark = null;
    } else if (storedHash) {
      setRotation(rotation);