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)

PDFViewerApplication.pdfThumbnailViewer.pagesRotation = evt.pagesRotation;
  PDFViewerApplication.forceRendering();
  
  PDFViewerApplication.pdfViewer.currentPageNumber = evt.pageNumber;
}
function webViewerPageChanging({ pageNumber, pageLabel }) {
  PDFViewerApplication.toolbar.setPageNumber(pageNumber, pageLabel);
  PDFViewerApplication.secondaryToolbar.setPageNumber(pageNumber);
  if (PDFViewerApplication.pdfSidebar.isThumbnailViewVisible) {
    PDFViewerApplication.pdfThumbnailViewer.scrollThumbnailIntoView(pageNumber);
  }
}
function webViewerVisibilityChange(evt) {
  if (document.visibilityState === "visible") {
    
    setZoomDisabledTimeout();
  }
}
let zoomDisabledTimeout = null;
function setZoomDisabledTimeout() {
  if (zoomDisabledTimeout) {
    clearTimeout(zoomDisabledTimeout);
  }
  zoomDisabledTimeout = setTimeout(function () {
    zoomDisabledTimeout = null;
  }, WHEEL_ZOOM_DISABLED_TIMEOUT);
}
function webViewerWheel(evt) {