This is the Add-on Compatibility Reporter (ACR) add-on.
ACR is an add-on for Firefox that lets you report whether add-ons are compatible/working or not. Mozilla monitors these reports and keeps an eye on misbehaving ones to take action to ensure Firefox users have the best experience.
Versions up to 1.1 were build using XUL add-on technology. This version, 2.0 and above, is built with the Add-ons SDK, available for download at: https://addons.mozilla.org/developers/builder
Project page: https://wiki.mozilla.org/AMO:Projects/ACR
Developed by Mozilla in collaboration with Briks Software: http://briks.si