Windows 7 Ultimate 32-bit SP1
Core2 Duo 2.26ghz
2gb ram
Thunderbird 24.6.0
Firefox 31.0

There seems to be a memory issue with Thunderbird that crops up when I've viewed videos using Firefox. I keep Thunderbird running all the time and everything's fine. But if I use Firefox to view a YouTube video or other video, it seems like after viewing the video (and maybe clicking on some related videos... it's sometimes hard to resist), Thunderbird's memory usage goes up dramatically. At some point, the memory usage gets to the point where it consumes the computer's available memory and Thunderbird becomes non-responsive. It seems to me that there might be some sharing of memory between Thunderbird and Firefox that becomes a problem when using Firefox to view videos. I try to remember to shut down Firefox after just about any browsing session but sometimes I forget.

Here's a screen capture that shows Thunderbird's memory usage... top is with Thunderbird in not responding mode, bottom is after restarting Thunderbird.