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)

offsetY,
          scaleX,
          scaleY,
          subtype: group.smask.subtype,
          backdrop: group.smask.backdrop,
          transferMap: group.smask.transferMap || null,
          startTransformInverse: null, 
        });
      } else {
        
        
        currentCtx.setTransform(1, 0, 0, 1, 0, 0);
        currentCtx.translate(offsetX, offsetY);
        currentCtx.scale(scaleX, scaleY);
      }
      
      
      copyCtxState(currentCtx, groupCtx);
      this.ctx = groupCtx;
      this.setGState([
        ["BM", "source-over"],
        ["ca", 1],
        ["CA", 1],
      ]);
      this.groupStack.push(currentCtx);
      this.groupLevel++;
      
      this.current.activeSMask = null;
    }
    endGroup(group) {