Rated 4 out of 5 stars

This version works with FF 7.01. Thanks to the developers!

http://verteksi.net/files/voikko/voikko-3.3/mozvoikko-2.0rc2.xpi

This review is for a previous version of the add-on (1.9.0). 

Development versions

The same version for Firefox 4 or newer can be found also at Add-On's Development Channel (https://addons.mozilla.org/en-US/firefox/addon/finnish-spellchecker/#beta-channel). To be released version (same as 2.0rc2) is still on the review queue.