Nice addon, not supported anymore though? Rated 3 out of 5 stars

Handy addon. It's unfortunate that it will no longer build addon installer files in the latest Firefox. Looks like it was updated 2011.

This review is for a previous version of the add-on (0.3.0.20110927). 

Alternatives

The original creator is no longer maintaining it, and I just agreed to take over in case I was inspired to make some modifications. However, Firefox is going in the direction of restartless addons which you can build using their online tools at https://builder.addons.mozilla.org/ . There are bugs with the feature to auto-upload from their site directly for submission to AMO (the official Addons site), but you can use the builder to download the file package (or just the source files) after you have built it and then upload the package to AMO yourself (assuming you want a public addon hosted by Mozilla). The online builder tool also doesn't support localization yet, but otherwise, you can do a lot using this tool.