From Fedora Project Wiki

Standard troubleshooting steps

Restart Firefox

Clear cookies and cache

Test in Safe Mode

    firefox -safe-mode

Reset preferences ( Safe mode option )

Troubleshoot plugins Disable plugins ( Ex: Adobe Reader, Flash, Java, QuickTime, RealPlayer, and VLC )

Make a new profile

   firefox -ProfileManager


Slowness when browsing?

Go to your profile folder and vacuum your db files

   cd $HOME/.mozilla/firefox/*.default/; for i in *.sqlite; do echo "VACUUM;" | sqlite3 $i ; done

Disable favicon and site-icon caching. Append do your user.js file:

   user_pref("browser.chrome.favicons", false);
   user_pref("browser.chrome.site_icons", false);

Turn off IPv6. Append to your user.js file:

   user_pref("network.dns.disableIPv6", true);

Disable dbus notifications within Firefox. Append to your user.js file,

   user_pref("toolkit.networkmanager.disable", true);

Turn off rich colour support. Append to user.js:

   user_pref("gfx.color_management.enabled", false);

Enable form colours. Append to user.js:

   user_pref("browser.display.use_focus_colors", true);
   user_pref("browser.display.focus_text_color", "#666666");