Firefox-all-spaces is a project mainly written in Shell, it's free.
Ugly hack to have a separate Firefox window visible on all Mac OS X spaces (workaround because afloat etc can't be used with Firefox)
If you read this on github the easiest way to install is to download the whole repos as a zip-file (press "Downloads" then "Download .zip")
This hack assumes you already have Firefox installed in /Applications.
To install drag "Firefox all spaces.app" to your applications etc.
First time you start create a new profile named "all spaces" and then exit the profile manager. DONT delete your default profile! Next time you start the "Firefox all spaces" application a new Firefox window will appear.
To make the new window visible on all spaces you have to add the Application in the "Expose & Spaces" preferences. Add it by clicking the "+" and choose "Other..." and browse to the application. It seams as this have to be done after each restart, don't know why.