S.O.S. for Mac OS (x)!!! Need to uninstal add-ons

In general, I am having a terrible time "uninstalling" Firefox add ons, extensions. I find many Firefox add ons enticing and helpful, but recently the frustration of removing an addon, frustrates me to the point that any joy I have received from FF add ons dissipates.

I have a Mac OSx 10.4 intel. Usually, the instructions I have read is to go to tools, click on add-ons and then go on and disable/uninstall. This doesn't work, for some reason. AFirefox sidebar, briefly blinks and then disappears and I am unable to do anything. Would greatly appreciate your help. Thanks