LJHook has made RP'ing easier, and unfortunately it has yet to be updated to work with the new version of FireFox. But fear not! A simple code hack serves as a walk-around until an official is released. All you have to do is edit the code in the install.rdf file and change the "Max Version" setting from 3.2 to 4.0. Simple enough, but not everyone is comfortable hacking this kind of code. Even knowing what to do it took me a few tries to make it work. With that in mind, I'm providing you lovely people the hacked file to make LJHook work in FF4, just follow these steps:
1. Download
this file, be sure you remember where you saved it to! File name is "livejournal_hook-3.2.2-fx.xpi" for easier reference.
2. Open up the Addons page in your FireFox. (Firefox menu > Addons)
3. Drag and drop the file you just saved into the Addons page.
4. Restart FireFox.
5. Enjoy LJHook again.
PS: I just tossed the file onto a MediaFire free account, so downloading it is kind of a pain, but it's the best I currently have. If anyone is willing to lend a little sliver of server space to let people download this more easily, you'd be amazing.