Having covered about Add-ons Manager UI and features in Firefox 4, let us take a look at how to uninstall add-ons in Firefox 4.
Uninstalling Add-ons in Firefox 4
1.Open add-ons manager from Firefox button>Add-ons
2.Click Extensions tab on the left side.
3.Select the add-on, click Remove to uninstall the add-on, restart if Firefox prompts.
Firefox 4 does allow undo of uninstall of add-ons if you change your mind after uninstalling particular add-on you can still keep it by clicking “undo” button offered by Firefox.