Ubuntu 9.04 ships with Firefox 2 as the default Web browser. You can install Firefox 3.5 (aka Shiretoko) through the Applications menu if you want. However, Firefox 3.5 breaks compatibility with the default Firefox 2 application handler. If you click on a package installation link and get a message that looks something like
Firefox doesn't know how to open this address, because the protocol (apt) isn't associated with any program.
Firefox Extension
Will automagically fix links to pdfs as your browse. Also adds a little icon next to each converted link. Props to Mattie for starting the ball rolling on this.
Install PdfMeNot 0.1.2
Ubuntu will not be upgrading the default Firefox package to 3.5 until Ubuntu 9.10. However, the universe repository in Ubuntu 9.04 includes a special firefox-3.5 package. At the time of writing this package contains an old beta release. It should be updated soon, but here’s a workaround if you can’t wait any longer.