We’ve had a few reports of this, and we know. The good news is the upgrade isn’t a huge amount of work, and it IS on our backlog. The bad news is that (obviously) it’s not done yet, and I don’t have an exact ETA when it will be. We’re working on finishing up a couple of really big projects at the moment, and they definitely take precedence over maintenance tasks.
We WILL make sure to let everyone know once the upgrade is done and the extension is working with Firefox 3.5.