After doing some analysis late last night and today to determine if we need a chemspill build, I have concluded that TenFourFox is not vulnerable to CVE-2019-17026, or at least not to any of the PoCs or test cases available to me. This is the 0-day that was fixed in Firefox 72.0.1 and 68.4.1. Though a portion of the affected code exists in the TenFourFox code base, there doesn't seem to be a way to trigger the exploit due to various other missing optimizations and the oddities of our JIT. (Firefox 45-based browsers using our patches as upstream should bear in mind this may not be true for other architectures, however.) Absent evidence to the contrary it will be nevertheless patched as part of the standard security fixes in FPR19.

http://tenfourfox.blogspot.com/2020/01/tenfourfox-not-vulnerable-to-cve-2019.html