"Clear the Cache": Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now" "Remove the Cookies" from sites that cause problems: Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes). See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

If it does work in Safe-mode then disable all your extensions and then try to find which is causing it by enabling one at a time until the problem reappears. You can use "Disable all add-ons" on the Safe mode start window. You have to close and restart Firefox after each change via "File > Exit" (on Mac: "Firefox > Quit")

I have already tried Clear the Cache": Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now" "Remove the Cookies" from sites that cause problems: Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Safe Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes). See Troubleshooting extensions and themes and Troubleshooting plugins

If it does work in Safe-mode then disable all your extensions and then try to find which is causing it by enabling one at a time until the problem reappears. You can use "Disable all add-ons" on the Safe mode start window. You have to close and restart Firefox after each change via "File > Exit" (on Mac: "Firefox > Quit")

But it still does not work

Try: Website colors are wrong Websites look wrong or appear differently than they should