Part of the Profile is corrupted and is not saving your preferences. https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

suggest read above but jump to here if feel it is correct. Create a new profile as a TEST to check if your current profile is causing the problem.

• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data
• https://support.mozilla.org/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over the problem. Never work with original files.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile
• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

Please let us know if this solved your issue or if need further assistance.

This might be something that is special for the Firefox version from the Ubuntu repositories.

Try the Firefox version from the official Mozilla server if you currently use a version from the repositories of your Linux distribution.

• https://www.mozilla.org/en-US/firefox/all/

Hi thanks for your replies. I never sign in to browsers, I never had to before the last update, it worked fine. I imagine that the second answer may be correct as I installed via sudo apt-get install, also it works fine in Windows but my Windows installations has never worked properly since Microsoft geo-blocked me when I moved country! That's why I use Linux. I don't know how to install from a different serer or from a downloaded file like that, but I'll look it up and figure it out. Many thanks/

Sorry! Looking more closely at the first answer I realise that I didn't understand what you were getting at! I have created a new profile but it didn't make any difference. If I have set Duckduckgo as my default search engine, can I be sure that this is what will be used? It's just a bit annoying that the Ubuntu mate homepage always has the google option selected even though I have removed it from the list in the search preferences.