It does what it says it will do, except not always. It can't load localfiles, which means you can't use custom HTML, JS homepages that are local on the machine. If this is possible to implement that would be a very welcome feature
Didn't seem to work at first, until I found out that due to Firefox restrictions, local files cannot be handled by add-ons. My homepage was a local file... I solved that by adding it to my (local) web server. A warning that local files are not allowed would have been useful!