Hey there, yes we have found (but still unsure why) Firefox 29/30 is crashing when using the CMS.
Investigated a bit and appears that 31 beta solves the problem suggest grabbing that or getting your clients to install until the official 31 stable comes out.
http://www.mozilla.org/en-US/firefox/channel/#beta
If anyone finds out the reason behind the crashes please post as we would be keen to know :)