"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")

This happened for on first use of a new laptop when windows gives you the option to select a web browser. I will try to correct it.

Clearing the cache worked for me

Clearing the cache worked for me too.

Doesn't work in safe mode for me. Have tried clearing the cache, but that has made no difference.