Most likely it won't need major updates to work, so I would imagine it's just a matter of the folks at google updating it so that it understands that it is compatible. That said, it's something the folks at google would need to do. I would guess that it wouldn't take them more than a couple days; but I really can't say for sure.

I just partially tested the Google Toolbar 7.1.20110512W in Firefox 5.o and it seems to work fine for the features I looked at.

If you install this extension, the GTB will be enabled.
https://addons.mozilla.org/en-US/firefox/addon/add-on-compatibility-reporter