There are several ways to forcefully enable disabled or "incompatible" addons in Firefox, but they ultimately do the same thing. I recently started having issues with the 32bit version of Firefox, stealing 1GB - 1.5GB of memory from my system if I had more than 3-4 tabs open. (I usually average about 8 - 15) Knowing the 32bit probably wasn't handling the memory right, I decided to try out the nightly x64 build to see if it would help my memory situation. (At the time of this writing, an official x64 release was not available) I will say that I've been pleasantly surprised that it not only solved my memory issue, but it's run extremely stable to the point that I use it for all of my web development on a daily basis. One plugin I use frequently is ColorZilla, an eyedropper color picker. I've tried a few versions on Chrome and still like ColorZilla better. Anyway, it quit working with the nightly builds and started stating that it was "incompatible" and remained disabled. After about a month of being disabled, I finally decided there had to be a way to force an addon through firefox and sure enough, there is.
I have two methods, the first is by far the easiest, the second is more of the nuts and bolts of Firefox which is the same thing the first method does, but it does it for you. I did run into one addon "Fire Sheep" that still remained disabled, but I hardly use it so I didn't really care. Just keep in mind these methods "may" not help...
1) Download and install: Nightly Tester Tools
2) Restart Firefox (If you haven't already)
3) Find "Nightly Tester Tools" in the menu structure
- Firefox Start Bar -> Nightly Tester Tools
- Tools -> Nightly Tester Tools
4) Click "Force Addon Compatibility"
5) Restart FireFox
At this point, all (or most) of your disabled or incompatible add-ons, should be enabled with a warning that it is incompatible.
1) Open the about:config window (click ok to proceed...)
2) Right Click and choose New -> Boolean
3) Choose from the list below, the right extension.check name for your situation and insert it into the box.
4) Set the value to false
5) Restart Firefox
Outside of the obvious versions, If you are running a nightly or something a little out of the ordinary, you might have to play with a few of these settings...
extensions.checkCompatibility extensions.checkCompatibility.3.6 extensions.checkCompatibility.3.6b extensions.checkCompatibility.3.6p extensions.checkCompatibility.3.6pre extensions.checkCompatibility.3.7a extensions.checkCompatibility.4.0b extensions.checkCompatibility.4.0p extensions.checkCompatibility.4.0pre extensions.checkCompatibility.4.2 extensions.checkCompatibility.4.2a extensions.checkCompatibility.4.2a1 extensions.checkCompatibility.4.2a1pre extensions.checkCompatibility.4.2b extensions.checkCompatibility.5.0 extensions.checkCompatibility.5.0a extensions.checkCompatibility.5.0b extensions.checkCompatibility.6.0 extensions.checkCompatibility.6.0a extensions.checkCompatibility.6.0b extensions.checkCompatibility.7.0 extensions.checkCompatibility.7.0a extensions.checkCompatibility.7.0b extensions.checkCompatibility.8.0 extensions.checkCompatibility.8.0a extensions.checkCompatibility.8.0b extensions.checkCompatibility.9.0 extensions.checkCompatibility.9.0a extensions.checkCompatibility.9.0b extensions.checkCompatibility.nightly
These are the entries that were installed by "Nightly Tester Tools". At the time of this writing, it stopped at v7.0b. I went ahead and added v8 & v9. By this point, you should get the idea of what you need to manually add. In my case of using the 12.01a nightly builds, the required value that I needed was: extensions.checkCompatibility.nightly
There are additional resources on the topic, I've pulled some of my information from those areas. I've documented this issue solely for the purpose of archiving the method needed to solve this problem for future instances.