That may mean the computer's CPU may be overworked. Start '''[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Firefox in Safe Mode]''' {web Link} by holding down the '''<Shift><br> ''(Mac=Options)'' ''' key, and then starting Firefox. A small dialog should appear. Click '''Start In Safe Mode''' (not Refresh). Is the problem still there? '''https://support.mozilla.org/en-US/kb/websites-look-wrong-or-appear-differently''' '''https://support.mozilla.org/en-US/kb/firefox-slow-how-make-it-faster''' '''https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix''' '''https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding''' '''https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding'''