Do you have "Work Offline" checkmarked in the Firefox File menu?

It can also be caused by the Ask Toolbar. See Problematic Extensions

No, I do not.

I also don't have the Ask Toolbar installed, so that can't be it; nor do I have any of the listed problematic extensions.

Could you try starting Firefox in Diagnose Firefox issues using Troubleshoot Mode please. If it works correctly in that configuration, then one of your add-ons is the culprit.

I'm still getting the same error, even in Safe Mode. The word "chrome" always seems to be mentioned, could it be referring to Google Chrome? I've tried reinstalling Firefox and deleting Chrome but that didn't help either. Perhaps my OS is the problem.

In this particular case, 'Chrome' has nothing to do with Google Chrome. See Chrome registration failed

Is that the error message you're seeing by any chance?

Unfortunately, no. The error message I keep getting is jar:file:///C:/Program Files (x86)/Mozilla Firefox/omni.jar!/chrome/en-US/locale/browser-region/region.properties..

I even tried running Firefox as administrator, it didn't help.

Type about:config in the location bar at the top, then type keyword.URL in the filter at the top.

Then double click the entry and remove whatever you find in there which will return it to "Default" and "String".

Then close Firefox via File | Exit.

Restart and then try typing one of your queries again.

That did it, it's working now. Thanks for the help, Xircal!

You're welcome.