There was a plan to turn the Firefox add-on install dialog into a doorhanger dialog (bug 588266). This was abandoned in favour of an approach using tabs (bug 643020). Rather than let the work for the former approach go to waste, we are releasing it as an add-on.
Run the 'build.sh' shell script and install the generated XPI file in Firefox.
You can install the latest release version at Mozilla Add-ons.
You can also clone the project with Git by running:
$ git clone git://github.com/brianking/Pretty-Install