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)

*   located. Include the trailing slash.
 * @property {boolean} [cMapPacked] - Specifies if the Adobe CMaps are binary
 *   packed or not.
 * @property {Object} [CMapReaderFactory] - The factory that will be used when
 *   reading built-in CMap files. Providing a custom factory is useful for
 *   environments without Fetch API or `XMLHttpRequest` support, such as
 *   Node.js. The default value is {DOMCMapReaderFactory}.
 * @property {boolean} [stopAtErrors] - Reject certain promises, e.g.
 *   `getOperatorList`, `getTextContent`, and `RenderTask`, when the associated
 *   PDF data cannot be successfully parsed, instead of attempting to recover
 *   whatever possible of the data. The default value is `false`.
 * @property {number} [maxImageSize] - The maximum allowed image size in total
 *   pixels, i.e. width * height. Images above this value will not be rendered.
 *   Use -1 for no limit, which is also the default value.
 * @property {boolean} [isEvalSupported] - Determines if we can evaluate strings
 *   as JavaScript. Primarily used to improve performance of font rendering, and
 *   when parsing PDF functions. The default value is `true`.
 * @property {boolean} [disableFontFace] - By default fonts are converted to
 *   OpenType fonts and loaded via `@font-face` rules. If disabled, fonts will
 *   be rendered using a built-in font renderer that constructs the glyphs with
 *   primitive path commands. The default value is `false`.
 * @property {boolean} [fontExtraProperties] - Include additional properties,
 *   which are unused during rendering of PDF documents, when exporting the
 *   parsed font data from the worker-thread. This may be useful for debugging
 *   purposes (and backwards compatibility), but note that it will lead to
 *   increased memory usage. The default value is `false`.
 * @property {boolean} [enableXfa] - Render Xfa forms if any.
 *   The default value is `false`.
 * @property {HTMLDocument} [ownerDocument] - Specify an explicit document
 *   context to create elements with and to load resources, such as fonts,