System: OS X El Capitan Version 10.11.6, Macbook Pro 16GB Preconditions: 1. Firefox is installed 2. Nightly is installed 3. Vidyo is installed 4. Default email reader in mail.app is set to Firefox (not Nightly) Steps to reproduce: 1. Nightly is open 2. Vidyo is open 3. In Vidyo, navigate to room listing, select my room, click on email icon Actual results: 1. Nightly handled the mailto: call and went cray cray. Tabs kept opening…looping…couldn’t kill…Nightly takes all focus. Was this reproducible? Yes, even in 58. See .mov for more

FWIW, I was able to reproduce this in 55.

Paolo, any ideas on how to debug what's going on here?

I would assume this is a variation of bug 218257, in this case for protocol handlers. Sean, can you try renaming the "handlers.json" file in the profile folder while Nightly is closed and see if this helps? If it doesn't, it may be that we are using the default association from the operating system, which for some reason happens to be Nightly. In this case, you may try to go to the Nightly preferences and set a different action for "mailto:". Let me know!

Let's close. This is dup of the other bug referenced above. Thx.