The WAVE Toolbar is now available at the Mozilla Add-ons site - https://addons.mozilla.org/en-US/firefox/addon/6720

It will continue to be available here at wave.webaim.org, but making it available on the Mozilla site will give it more exposure.

Of note, it is listed as an ‘experimental’ add-on because it has not gone through Mozilla’s review process which apparently is taking several weeks right now. You can help by rating the toolbar and leaving a quick review.