The biggest gripe
my team has about the drupal APIs is that once you're inside a tree, you can't search easily. I've always wanted to try making my own Firefox extension - this seemed like an ideal starter project.
Initial specs were much larger; I built a section to let you add new Drupal sites to search on. We really wanted to get this out, so I removed those bits.
The result? You can quite easily search drupal.org, and all the trees of api.drupal.org . Not the most robust module, but it sure was fun to figure out how it all works. Most of the code was based on the Search Bar tutorial from borngeek.com.
Our next extension for release is much more ambitious. We've designed a UI for phptemplating theming xhtml/css pages within Firefox. Let me know if there are any features you think would be killer.