I've been hunting around for a good project to do while I freeload in Peter's Mac Development class. I'm just about to finish up my Thunderbird Growl and Spotlight integration bugs, and I'll be needing something new to do. Here it is: Bug 457546 - add Quick look support to Thunderbird.
Quick Look is one of those bits of polish in Leopard that makes you happy every time you have to use it. I love not having to fire-up applications just to do simple things, like viewing documents. I've only taken a quick look (I'm sorry, I couldn't help myself) at the way it's built and docs, but it seems to follow a similar plugin style to the indexers for Spotlight. You can see the list of plugins you have now, by doing this in terminal:
$ qlmanage -m
I'll probably need to write a generator for com.mozilla.thunderbird.mozeml files. However, doing the previews might be as straightforward as feeding attachments to qlmanage via nsIProcess. Try this with a doc you want to view:
$ qlmanage -p ~/Just/one/file.doc
$ qlmanage -p ~/Some/file.doc ~/Some/other/file.doc
Mail.app's built-in quick look button makes this so easy I have to do it in Thunderbird. I'll post on my progress as I go.