On some YouTube videos - for example, the link below - M5 refreshes a number of times, I assume switching between rendering engines, before the tab crashes. The reload and switch engine buttons do nothing.
had that, was add-on conflict\bug... "YouTube Center"
disabled it, and installed it via violetmonkey as script and not maxthon add-on, after that everything works just fine.
so if you use any add-on try that...