It's about time, they should also get rid of Web Start support. I would imagine those 2 account for a good chunk of the security alerts/updates over the years.
Firefox 44: 12 security fixes including 3 critical vulnerabilities
Firefox 43: 16 security fixes including 4 critical vulnerabilities
Firefox 42: 18 security fixes including 3 critical vulnerabilities
On the evidence so far, I’m not sure browsers, as they expand to try to do more of the things we used to use plugins for, will necessarily prove to be significantly safer than what we had before.