TypeError: null is not an object (evaluating 'browserSheet.insertRule')

[rhansen]

Client-side exception at src/static/js/cssmanager.js#L64 on latest develop (cb9f6d6). Seems to only happen on Safari. It doesn't always happen, so it appears to be a race condition. I had hoped that PR #4960 would fix it, but it did not.

[webzwo0i]

Do you have a trace to find out which makeCSSManager call caused it?