Issue 581997  fixed a crash in content scripts that use WebGL. The basic problem was that some implicit references that were set up between the JavaScript wrappers were over-specialized to the main world.

At the time we didn't write regression tests for this fix because it would have been hard; the existing extension tests (which I think are part of the browser_tests harness) don't run on the GPU bots, and the tests which do run on the GPU bots within the Telemetry harness don't load extensions.

We should revisit this issue and add some regression tests to the bots because otherwise this will inevitably regress.