• 1 Download Firefox Full Installer For All languages And Systemsv40 {web link}
• 2 Uninstall Firefox from your computer {web link}
  DO NOT remove your profiles.
• 3 After, reboot the computer. Then run the full installer.

https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Note: Some software, like Advanced SystemCare with Surfing Protection, can protect files in the Firefox profile folder against changes. If you have such software then check the settings or uninstall this software.

A possible cause is that you have the mouse pointer in a position that is within the drop-down that opens if you type a query. If the mouse pointer is in the wrong place then you can invoke the item under the mouse pointer instead of the query.

When I experiment with this, it depends on whether I bump the mouse while typing my query.

Simply having the search panel drop down behind the mouse pointer isn't enough to modify what happens when you press Enter. However, if you bump the mouse, you'll see that suddenly whatever is behind the mouse is highlighted. In my testing/experience, that's when the problem occurs. Firefox is gleaning intent from the mouse movement, but in such cases, it is just happenstance.

Hopefully someone will figure out a happy solution to this awkward keyboard/mouse interaction.

Wow, jscher2000, you're 100% correct that it has to do with the mouse - though in my testing it doesn't require mouse movement to reproduce.

If my mouse cursor just happens to be positioned such that - when the 'search dropdown' is opened by virtue of the search box getting focus - the mouse cursor ends up being over the "Change Search Settings" option...

then performing the repro steps will in fact result in that page of the settings being opened.

Using my "psychic debugging skills," I bet jscher2000 is running OS X. I'm running Windows.

Testing in OS X, since OS X hides the cursor when the user is typing, it's not as easy to repro this braindead behavior. It does require bumping the mouse, because then the cursor will appear, and may be over the "Change Search Settings" entry in the dropdown. (It's not a matter of Firefox trying to intuit user behavior - it's just dumb behavior.)

In Windows, however, the cursor is not hidden when the user is typing, meaning that the repro steps I describe at the top of this comment are sufficient.

Pretty ridiculous.

Thanks for leading me down the right path, jscher2000.

Actually, I run Windows 7, but I have seen someone say that vibrating the table enough to move the mouse pointer by 1-2 pixels will trigger the selection, so bumping might not be necessary. Still, just dropping the panel should not be enough to cause the problem.

Sorry cor-el - I didn't see your response until just now. I've re-marked it to be the accepted answer.

Thanks.