Created attachment 515566 [details] testcase ###!!! ASSERTION: Default canvas font is invalid: 'res == NS_OK', file content/canvas/src/nsCanvasRenderingContext2D.cpp, line 2885
This has nothing to do with moving between frames. This assert will fire any time you use a <canvas> that's inside a document with no presshell (as in this case). I personally think the assert is bogus (and that the behavior is possibly semi-bogus too).
It doesn't seem right to simply mute the assert, if the real problem is that we don't know how to deal with the font of a canvas in this situation - shouldn't we be fixing _that_ issue?
Created attachment 523905 [details] [diff] [review] wip1 I guess we could try harder to create something, also in the absence of a pres shell... is that what you're suggesting?
Comment on attachment 523905 [details] [diff] [review] wip1 I merged this into the patch in bug 647480...
Seems to have been fixed by the patch in bug 647480.