When you upgrade you version of Firefox some extension might stop working, however most of the times they will work fine with the new version of Firefox. There is an easy way to make Firefox stop checking for compatibility.
1. Open Firefox and type about:config in the address bar. Then click the button promising to be careful.
2. Right-click anywhere on the screen, choose: New > Boolean and name this boolean:
Press OK. Then set it to false and press OK again.
3. Now right-click again anywhere choose New > Boolean and make the name of this one:
and set the value of that one to false.