XPI corrupted after following instructions

[Jayinem]

I followed the instructions on the github main page added fx-folder into program files/mozilla firefox and added utils into appdata/roaming/mozilla firefox/profiles/ added chrome folder and put utils folder in it, refreshed the cache of Firefox and restarted but I am unable to install the latest xpi it appears corrupted msg hits every time.

Edit: oops it's for Tab Mix Plus. Thought this was the Tab Mix Plus github.
Am I doing something wrong or did Firefox do something? I had it working before but my Firefox got deleted and trying to re-install it. Using latest version and latest Firefox.