Re: Plugin-container.exe error
Plugin-container.exe is a process that runs parallel to firefox.exe. As the name suggests, it contains your plugins - it ensures that firefox doesn't crash everytime one plugin has a hiccup by keeping them separate.
If it's crashing often, it can be for any number of reasons.
-A lot of people have reported that the errors go away if you install and run CCleaner to remove temporary files.
-A corrupt plugin could be causing it to crash. Go through your plugins and try disabling them one by one to see if any of them are causing it.
-If all else fails, reinstall firefox. Your bookmarks and such should carry over.