I've had memory and crash problems for some time now and decided to create a reduced testcase to document hopefully-helpful data. My issues have often seem connected to images and recently HTML5 video has seemed a worse culprit. I suspect my GPU is somehow involved. I'm running Windows 7, Firefox 37.0a2. I created a fresh profile, set the homepage to six tabs of the same URL: https://www.youtube.com/watch?v=LizAjaOXi4U (defaults to 480p) Let the videos play for at least 30 seconds and closed them all leaving a blank tab and then waited and checked Firefox's memory usage in my process browser. The "resting" memory quickly climbs upward each time I open the six tabs. (FYI, when I started the fresh profile to just a blank tab I got 225 MB.) I was able to use this technique to crash the browser before, but recently somewhere around 1 GB I received the C++ runtime failure which I've attached. I get the error window 6 times (one for each tab), hitting 'Retry' kills Firefox and sent the following crash report: bp-3c512f0e-b308-4665-bd4c-9231c2150211 Hitting 'Ignore' makes the window go away without issue (before hitting ignore the video will be paused). Interestingly, after the error windows began, the memory ceases to climb after repeated opening of the youtube tabs (at least 3 cycles). After closing them with only about:newtab remaining, it hovers at 1.07-1.09 GB each time. Also notably I lost audio somewhere along the way (didn't notice when because I muted it because of multiple videos) and that audio was lost for my whole system until Firefox closed. I will attached a memory report I took during the testing. P.S. I just noticed somone on reddit post that they've been seeing the same error since last night: http://redd.it/2vl25h

Thanks so much for reporting this. We found and diagnosed the issue today as well. The fix is over in bug 1131768, so I will dupe this bug against that one. Please try the memory issue with tomorrow's build and open a new bug if it still occurs. Thanks for helping make Firefox better!!!