It will be a few days before it hits testing, but in Sid we just got the firefox-esr instll paired with the iceweasel update. A decent explanation of it is at
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=815006
I had no problems, except I will have to update my bookmarks as I had been using chromium much more lately. I am sure that others in Debian will be writing up various things about this and how to have a more recent Firefox.
peace out,