Rated 3 out of 5 stars

Firefox: 3.6.18
No harm done; the button appeared; I pressed it, and after some time... nothing happened. On my firefox, compatibility checking is turned off, and there are over a 100 extensions, so maybe that's why nothing happened.

It doesn't disable extensions

Sorry for your troubles, but it wasn't IIC that disabled your extensions. IIC doesn't modify extensions at all; it is, effectively, a read-only extension (it only modifies what is displayed in the addons window). I tried installing it from AMO in a FF3.6.18 install, and it worked perfectly. Could you enable your modified extensions, reinstall IIC, and say if the same thing happens again?