While a zero day is interesting news, I think a more interesting point is that the bug was reported by Qihoo 360. The company has a bit of a storied history when it comes to security: https://en.m.wikipedia.org/wiki/Qihoo_360
"In January 2020, a Reddit user reported Qihoo's presence in Samsung mobile phones as a pre-installed storage cleaner in the device settings, from where it sends data packages to Chinese servers."
Definitely not a company one would expect to report vulnerabilities. Also odd that they would be find Firefox issues given their browser uses IE and Chrome renderers.