This morning Ubuntu’s UpdateManager ran and informed me of 1 update to do with the Adobe flash player. I let it install…and promptly I no longer had the Flash player in Firefox 🙁 An ‘about:plugins’ confirmed that it was missing.
By following the setup and then removing flashplugin-nonfree, then adding it again, the Flash player reappeared in my Firefox. Fixed in 2 minutes.
After this I removed the ‘proposed updates’ from Software Sources (added via the bug-report’s instructions) and all seems to be well.