One of the reasons Firefox is a popular browser is the support for thousands of add-ons. Add-ons will give extra functionality and features, but at the same time might slow down your PC. Even if you uninstall them, it might still leave the preferences behind. eCleaner is an add-on for Firefox designed to clean up the traces left by extensions after uninstallation. Once installed, you can open the options and view the preferences left over by extensions.
You can select the add-ons from the list and click on the Clear selected button. This will remove all the left over preferences from the uninstall. Cleaning these left over preferences might speed up Firefox as add-ons are one of the primary reasons for slowing down Firefox.
The add-on is currently in its primary version and the author has mentioned that more features could be on the way.