Spellbound is a great spell check addon for Mozilla Firefox. It works for any web text entry area. My friend justice had showed it to me quite a while ago, but it didn't work when I was using htmlarea so I hadn't used it much.
I just reinstalled spellbound, and am happy to say it works on shadyvale.org when using the new rich text editor. So install the spellbound addon, and blog without questioning spelling till your done writing. Then right click, and select "check spelling", or hit ctrl-shift-F7.
Note: Installation is a little funky if your on Linux, because you'll most likely need to log in as root to install the libraries and dictionary for the extension. Simply log in as root, load up firefox, and go back to the install page. For some reason they need to be in your firefox install tree, and therefore when you upgrade firefox, you'll probably have to reinstall as well.
Oh, and while I am at it, if you haven't already, upgrade to Firefox 1.0.5.


