Troubleshoot Mode runs Firefox with some features and customizations disabled (see below for details) If you’re having a problem in Firefox that does not occur in Troubleshoop Mode, the cause of the problem is one of the disabled items. The most likely cause is an extension, theme or hardware acceleration. See this article for solutions: If Firefox keeps starting in Troublehoot mode, see Firefox is stuck. If you want to test Firefox’s behavior, you’ll want to see if the problem goes away.”]
Source: https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode