Disabling extension compatibility checking can take care of a lot of this stuff. Just go to
about:configand right-click to create a new Boolean entry. Name it
extensions.checkCompatibilityand set it to false.
This will allow you to install any extension. Most will work, but some that are badly out of date may not work completely or at all. Some may even crash the browser, in which case you'll have to edit some text files and delete some directories in your profile to salvage it. But that can be done inside of two minutes if you know what you're looking for.