I used to use the Aurora builds of Firefox, but now I've uninstalled Firefox and gone back to Chromium. I've removed the PPA, but it still shows up under "All Software" in the Ubuntu Software Center, when I click on the arrow to the side of it to display my PPAs. I've checked the Software Sources to see if there's anything leftover, and there's nothing. I use Y PPA Manager, and there's nothing there to remove as well. How do I get rid of it?
I'd check that it doesn't show up in your apt sources list in /etc/apt/, then run an apt-get update from a terminal and see if the problem persists.