Interestingly, the part that crashed Firefox was one of the simpler tests--typing a bunch of text content in, then resizing and rotating the shapes that contain that text. Firefox didn't give any details as to why it crashed.

The only thing I could even measure that would lead to a crash is memory usage. I just re-ran the test and watched the process's memory usage. It hovered in the 300-400MB range during the first third of the test. Then, during the test I describe, memory usage rocketed to around 1GB, at which point the browser crashed hard.

I'm not sure why Firefox would exhibit this behavior when other browsers don't, but we know a few people at Mozilla (they're customers of ours) so we'll probably reach out.