That would be from an extension, anything similar from Firefox would have been cleaned up. If you'd been on 4.0.1 for a while and it just started happening, then I'd try Tools > Add-ons > Extensions then on the gear wheel choose "View Recent Updates" the date will appear the list small and the. The "last updated" button near top right does something mysterious. To see list in normal fashion again choose "Appearances" then return to "Extensions". If you dislike the formatting of the Add-ons list during normal viewing you can improve it tremendously with a custom style: * [https://addons.mozilla.org/firefox/addon/stylish/ Stylish :: Add-ons for Firefox] * [http://userstyles.org/styles/42112/firefox-4-compact-addons-manager Firefox 4 - Compact Addons Manager - Themes and Skins for browser - userstyles.org] From the wording the message could possible be referring to a Collection of Extensions. I avoid collection sets like the plague. Also see related answer * [https://support.mozilla.com/en-US/questions/824098 i keep getting a pop up saying uninstall set | Firefox Support Forum | Firefox Help] by Cor-el.