ppa:mozillateam/firefox-next in my Software Sources, but even though Firefox 9 beta got released, my system still has Firefox 8! Why is this, and how do I get the latest?
The "ppa:mozillateam/firefox-next" should soon have Firefox 9beta1, and hen its ready, you'll be prompted to update.
If you want to, download a beta directly from Mozilla.
Update: Firefox 9b1 has been published in the PPA on November 16.
Sometimes, the guys running the firefox-next PPA run into some problems getting it built, which I think is the case now. You can manually check the status of their builds at https://launchpad.net/~mozillateam/+archive/firefox-next/+packages. Eventually, they'll fix it (they always do), but until then, you could:
press ctrl alt t to open a terminal window and do the following commands.
sudo add-apt-repository ppa:ubuntu-mozilla-daily/ppa
sudo apt-get update
sudo apt-get install firefox-trunk