I use this add-on all day, every day.

I use the same Extension in Google Chrome as well (obviously, the version from the Chrome Web Store).

It does exactly what it says it will and doesn't require much set-up (although there's a lot of inherent power in it if you understand things like Regular Expressions).

For anyone who's struggling to get it working, the Developer appears to be responsive and super-helpful on the "Support site" link in the "More information" section of the add-on's page at mozilla.org: https://addons.mozilla.org/en-US/firefox/addon/redirector/