How do you reproduce the bug? I tried this and I only see one CSS warning in the Web Console and in the Error Console.
STR: - open test.html in a new tab - switch to the tab - wait until the page is loaded - open the web console Actual Result: - JS warning "unknown property"
Ah, so I have to open the Web Console after the error happens. Thanks for the STR. I was able to reproduce now. I have a hunch what's causing this. Will look into fixing it ASAP.
Created attachment 636374 [details] [diff] [review] [in-fx-team] proposed patch This fixes the problem for me. It is an embarrassingly simple fix: I passed the wrong argument to the function that determines the cached message category. Thanks for your report!
Thanks for the r+!
Comment on attachment 636374 [details] [diff] [review] [in-fx-team] proposed patch https://hg.mozilla.org/integration/fx-team/rev/e42cc35e45cc