hello, maybe it's an issue with the protected mode in the flash plugin - you could try if [https://support.mozilla.org/en-US/kb/flash-113-crashes#w_solution-2-downgrade-to-flash-10-3 downgrading to flash 10.3] (which is still supported) or [http://forums.adobe.com/thread/1018071#TemporaryWorkaround disabling protected mode] makes a difference.

Your post did not include much information about your Firefox setup, so here is some general advice. This is some standard guidance that addresses the most common issues with the Flash player on Windows: (1) Disable hardware graphics acceleration in Firefox and in Flash. Driver updates can create incompatibilities even if Firefox ran normally before. (A) In Firefox, un-check the box here and restart: orange Firefox button (or Tools menu) > Options > Advanced > General > "Use hardware acceleration when available" (B) In Flash, see this support article from Adobe: http://helpx.adobe.com/flash-player/kb/video-playback-issues.html#main_Solve_video_playback_issues (2) Disable protected mode (Win Vista / Win 7 / Win 8) See this support article from Adobe under the heading "Last Resort": [http://forums.adobe.com/message/4468493#TemporaryWorkaround Adobe Forums: How do I troubleshoot Flash Player's protected mode for Firefox?] ---- When Firefox crashes, information about the crash often is stored and can be viewed by entering '''about:crashes''' into the address bar and pressing Enter. If you agreed to submit crash information to Mozilla, you can click a crash ID to view your crash on the server and sometimes helpful information about causes. I say sometimes helpful because new types of crashes might not have a diagnosis and often the information is difficult to understand. You could try pasting some recent crash IDs into a reply here for volunteers to review. ---- As a temporary workaround, you can try using the FlashBlock extension to prevent Flash from running except when you want it to run. This should reduce surprises on pages that run Flash, for example, as part of their Google Analytics scripts. https://addons.mozilla.org/firefox/addon/flashblock/ ---- One issue people have identified with YouTube in particular is a conflict with certain AdBlock Plus rules. I haven't kept track of the details, but if the problem becomes limited to YouTube, definitely try making an exception if you use that extension.