There are pauses, even worse than in Chrome. Use MemChaser add-on to see GC activity in FF. In Firefox Nightly on the particle demo I have non-incremental 0.6-0.7s pauses every ~10s (not to mention stutter from incremental GC in between the big pauses). In Chrome on the same sample I just don't have any pauses longer than 0.1-0.2s (every ~2s).