It seems at least Leethax hack has been fixed (sort of) according to the messages section on
The steps to make it work again are:
1. Download Fantazyn's leethax.xpi patch:
2. Open Firefox (if it isn't already running)
3. Drag the leethax.xpi file onto the browser window
4a. If it installs, go to 6
4b. If it tells you it can't load it or for some reason it doesn't work go to 5a
5a. Enter into the search bar: about
:config
5b. Promise not to do anything stupid
5c. In the search box type: xpinstall.signatures.required
5d. Change it to False
5e. Restart Firefox
5f. Drag the leethax.xpi file onto the browser window
6. Restart Firefox
Fingers crossed the lockbox hack fix comes out soon!