Firefox scored below Chrome and Safari in several areas: address space layout randomization (ASLR), heap protection, stack guards, fortified source. And I've even seen infosec people saying that Firefox has some of these, but doesn't even enable them on builds for some platforms!
https://theintercept.com/2016/07/29/a-famed-hacker-is-gradin...
They give one example (with a graph) of the security mitigations that are in popular web browsers:
https://prod01-cdn07.cdn.firstlook.org/wp-uploads/sites/1/20...
Firefox scored below Chrome and Safari in several areas: address space layout randomization (ASLR), heap protection, stack guards, fortified source. And I've even seen infosec people saying that Firefox has some of these, but doesn't even enable them on builds for some platforms!