Used it to force firefox to use port 8080 instead of 80 for a specific site. At first it seemed to work alright, but then I saw that when submitting form data it doesn't perform the redirect.

The latest version available when updating is 3.1.0 (updated on August 5 2016), which isn't working with FF 48.0 (redirection rules aren't saved).

Update:

Found out what's causing the problem. The addon "RequestPolicy Continued 1.0beta12.3" prevents Redirector 3.1.0 from working properly.

When I go to create a new redirector, the Save button is greyed out. Should I use an older version that's compatible?

It does not work in the last days on Firefox 48 + Redirector 3.1.0.
Not saved settings redirects.

Does exactly what it says on the tin.