close browser option missing

It should be there. Please read How do I quit Firefox for Android?.

I noticed this as well on Firefox for Android.

It seems the old “Exit browser” option is no longer directly available in settings. From what I understand, Firefox has moved toward managing background activity automatically, so the app doesn’t need a manual close option like before.

Right now, the closest behavior is just swiping the app away from recent apps if you want to fully close it, but even then Firefox may still keep some processes for performance and sync.

If anyone has found a new hidden setting or workaround for restoring a full exit option, it would be great to know.

No, it's still available as before, only if something is selected in the Delete browsing data on quit menu. Please read the article attached earlier to check the settings.