Looking forward to installing this as soon as Firefox 4 is available to Linux users! Otherwise, any plans to supporting earlier versions of Firefox?
Missing e is built using a SDK (software development kit) created by Mozilla for called Jetpack. In my opinion, it is a huge improvement over Firefox’s add-on API. It allows you to develop extensions much like in Chrome.
While the original Firefox add-on API is certainly more powerful, Jetpack makes developing add-ons that communicate between injected scripts and a background process (the model that Missing e uses) much simpler.
Jetpack only supports Firefox 4 and above, and almost assuredly never going to support earlier versions. Porting Missing e to the older add-on API would likely be a painful experience that will be less and less valuable the more time passes.