The template "crashsig" does not exist or has no approved revision. NPSWF32.dll
If Firefox is crashing when you try to view videos on YouTube, it is usually caused by the Flash plugin conflicting with one of your extensions.
Firefox 3.6.4 and above load plugins separately from Firefox, allowing Firefox to stay open if a plugin crashes. To make sure you are using the latest version of Firefox, see Update Firefox to the latest version.
Firefox extensions can cause this crash. To test whether your crash is happening because of an extension, try launching Firefox's Troubleshoot Firefox issues using Safe Mode: Click the menu button , click help and select Restart with Add-ons Disabled.... Firefox will start up with the Firefox Safe Mode dialog.
The NPSWF32.dll file is associated with the Flash plugin. If the crash still happened in Firefox's safe mode, try uninstalling and re-installing the Flash plugin: