Bug 29379 – printing from firefox 3 ( ff3 ) issues indeed appeard to be fixed in 5.0.10 (we skipped 5.0.9), and we have not seen it reappear in 5.0.11.
This thread is unrelated, and per #8 and #9 is not actually a problem introduced in 5.0.11. The sender happened to change their newsletter format at around the same time that harpo updated to 5.0.11, but that's just a coincidence; the new newsletter breaks in all ZCS versions, and the old newsletter works in all ZCS versions.
For the fixes that I considered important post-5.0.8 see https://carltown.carleton.edu/rgraves/weblog
Newly broken in 5.0.10, and still broken in 5.0.11, is "View Mail" for resources from the Admin console, Bug 32120 – view mail on alias or location or resource opens admin console
Other than 32120, I don't know of anything newly broken post-5.0.9.