If you have Firefox, then it seems like you need to update it. It is reported that Firefox is attacked by a critical bug. Mozilla has released security updates Firefox 67.0.3 and Firefox ESR 60.7.1 to fix this bug. This bug is capable of getting exploited to take control of vulnerable systems.
So, it is clear that Firefox, being one of the best mainstream web browsers for security and privacy-minded users these days, can also succumb to such unforeseen exploits.