To configure an extension, open the Tools menu, click on the Add-ons Manager, switch to the Extensions page, look for the extension, click on it, press the Options button (if it has one), and start tweaking. Or, click on the Options Menu button, select the extension, and start tweaking.
That’s four steps less thanks to the handy Options Menu, a Firefox extension developed by James R Skinner, that gathers all your extensions’ options dialog into a single menu you can add to a toolbar or the Tools menu, for real quick access.
Don’t need all your extensions in the menu, or want them all there whether they have an options dialog or not? Options Menu has an preference for that and more.
Very handy, complete and unobtrusive. Get Options Menu from Mozilla Add-ons.