beware of offsite postings Rated 2 out of 5 stars

If the author says its compatible with FF3, then there should not be anyone posting offsite links to modded versions. Beware of the links provided by users that reside on sites that are notoriously for warez and virus/trojan infested programs. If someone can integrate on a DOM level with your browser, there is no limit to how hard they can screw you with it. If you ever find something that is not "compatible" because the author didn't increment the version but you know it works with your version (Compatible with FF3 will also works with FF3.x.x even if the author doesn't say so) then open up the XPI using Winzip or Winrar (its nothing more than a zip file) and then extract the file install.rdp and open it using Notepad/Wordpad (its nothing but a text file) and go to Max Version section and change to 3.* and save the file. Then replace the file inside the XPI with this one and then open the XPI in Firefox and install it. Don't trust outside mods that can have more than you bargained for, take it from a programmer of more than 15 years and a good Samaritan.