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)

webViewerResetPermissions();
    this._fellback = false;
    this.store = null;
    this.isInitialViewSet = false;
    this.downloadComplete = false;
    this.url = "";
    this.baseUrl = "";
    this.documentInfo = null;
    this.metadata = null;
    this._contentDispositionFilename = null;
    this._contentLength = null;
    this._saveInProgress = false;
    this._cancelIdleCallbacks();
    promises.push(this.pdfScriptingManager.destroyPromise);
    this.pdfSidebar.reset();
    this.pdfOutlineViewer.reset();
    this.pdfAttachmentViewer.reset();
    this.pdfLayerViewer.reset();
    if (this.pdfHistory) {
      this.pdfHistory.reset();
    }
    if (this.findBar) {
      this.findBar.reset();
    }
    this.toolbar.reset();
    this.secondaryToolbar.reset();
    if (typeof PDFBug !== "undefined") {
      PDFBug.cleanup();
    }
    await Promise.all(promises);