Compatability Fix Rated 5 out of 5 stars
I love this theme. Can't use Firefox without it. When I updated the the latest version (6.0.2) and tried to update RedShift, firefox wouldnt download it because it "wasn't the addon Firefox was expecting".
For anyone else with the same issue and for people who don't want to "install an add on to install an add on!" this is the easiest solution:
You need to install it manually.
Don't just click 'Accept and Install' to download the latest version. Instead right click on the button and select 'save link as..'
Save it to your computer.
Then go to Firefox/add-ons and click on the gearwheel sign. There you select "install add-on from file" and choose the saved add-on file. It is redshift_v4-6.0-fx.
Enjoy using the theme again.
(credit to 'lexkamaci' at shift-themes.com)