If Firefox starts up after an update without your bookmarks and other settings, check whether your data is available in a different profile:

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it. The About Profiles page will open. This page should list at least one profile and could list many.

The profile that Firefox is currently using will show:
This is the profile in use and it cannot be deleted.

Please do not delete anything here; don't use any Remove buttons.

Do you have another profile named default or default-longnumber listed on this page? If so, you can check whether it is the one you were using recently by clicking its Launch profile in new browser button.

If it isn't what you want, simply close that new window.

If it IS what you want, click the Set as default profile button for that profile on the about:profiles page. Firefox will use it automatically at the next startup.

For more information see Recover user data missing after Firefox update or reinstall.

Note: If your bookmarks are not available in another Firefox profile, see Recover lost or missing Bookmarks for other solutions.

This is rubbish! You shouldn't have to do anything after an update! You wouldn't expect to have to rebuild your house after remodeling a bathroom! Or rebuilding the engine in your car after upgrading the stereo! It is so stupid that updates reset personalized settings at all!

That’s honestly poor update handling your data shouldn’t get wiped unless something’s seriously broken, and even then there should be safeguards. Most of the time it’s due to profile corruption, sync issues, or updates overwriting local files without proper checks. Developers keep pushing features but ignore user control, which is the real problem. People expect systems to adapt to them, not the other way around—same mindset you see when someone looks for home improvement Baltimore services, they want customization, not forced defaults. Browsers need to fix this at the core instead of patching it every few releases.