Firefox regularly freezes for a minute or more, mostly in gmail
Firefox sometimes freezes for one or two minutes. During this time it doesn't respond to anything. It uses a little over 100% CPU (one of four cores) during this time, and around 1GB memory. I don't get a "stop script" message. No other programs I use have this behavior.
This is rare except in Gmail, where it happens every 10 minutes, often when moving the text cursor by clicking somewhere in an email I'm typing.
I use Firefox 40.0.3 on Ubuntu 14.04. I just tried and the problem also happens in safe mode, although the two freezes encountered were short (seconds instead of a minute). Normally I use several addons, mostly very popular ones not specifically related to Gmail/Google. I often have ~10-15 (pinned) tabs open, though I didn't in safe mode.
I already deleted my profile, then synced on a clean profile.