Hi, hold down the Shift key when you start Firefox to start in Safe Mode. More - Diagnose Firefox issues using Troubleshoot Mode.

If it works in Safe Mode, disable any theme or add-ons - Add-ons Manager (Ctrl+Shift+A) > Themes/Extensions and restart Firefox; then if it's OK, re-enable them one by one until you find the culprit. You may need to restart Firefox after enabling some add-ons.

If that doesn't help, have a look on the Google results page > Settings > Languages.

If your question is resolved by this or another answer, please take a minute to let us know. Thank you!

Thankyou for your suggestion but it was only useful inasmuch as I wasn't aware of a Firefox Safe Mode. It could be useful in the future. My preference for my home page is still correct in my Options but Firefox just doesn't take me there. I have discovered that if I use a VPN set to UK then Google will open correctly. I guess that is a fix of sorts but doesn't really address the question of why all my previous versions of Firefox didn't need a VPN to work properly. I may just reinstall the old ESR version as I don't find Quantum of any particular advantage.

Are you located in France?

What Firefox language version do you use?

Does it make a difference if you set en-gb as the first language?

Yes, I am located in France. My OS and all my installed software is set with UK English as default. I have just installed Opera and the problem does not appear. I can go straight to Google.co.uk when the browser is opened. Firefox will no longer do it.

I find that odd if you set the homepage it shouldn't change unless your ISP does the settings for you. I think it has more to do with a bad install possibly did you uninstall all FF and delete the Mozilla folder and reinstall to see what happens?

Yes. It was a clean install. I have since posted this problem on another (non-technical) forum and other people have had the same problem.