Upon upgrading to the Firefox 1.5 1 beta release many of my extensions did not work. Not knowing why I did a few searches. After just what seemed like nanoseconds I found an article on Roachfiend.com that outlined a simple fix and an helped me understand how firefox extensions work.
By simply changing the child node inside install.rdf to 1.5 (the 1.5 beta version) my pagerank extension now works with 1.5. Example: < em :maxVersion>< strong>1.5< /strong>< /em>
Note: This works on extensions that have almost nothing to do with the new browser code.