FWIW, my phone and the Play store on the web are now out of sync too. In the browser, it said Firefox is up to date. On my phone, there is an available update.
Also, the app I tried to download (which immediately failed) is nowhere on my phone, but the Play store on the web says it's installed. If I try to uninstall it, I just get an error.
Oddly enough, after a reboot I was able to update Angry Birds Star Wars, but nothing else works.