And what is the error saying to your screen shot not what is being discussed in Bug 1418594.

raconnor said

Apparently this is discussed in Bug 1418594. I have turned off the Exploit detection in Malwarebytes as a TEMPORARY solution. Hope to hear of a fix/repair/upgrade from 58.0 to this problem soon.

It may not necessarily be a issue with Firefox 58.0. Also the “RET ROP Gadget detection” in Malwarebytes is not checked by default.

https://forums.malwarebytes.com/topic/219551-firefox-58-malwarebytes-anti-exploit/ and Malwarebytes had a issue with Firefox 58.0b4 back in November https://forums.malwarebytes.com/topic/215365-firefox-quantum-beta-v-580b4-64b-closed-by-malwarebytes-v-3312183/

Turning off a security feature, even if it is one that is not ON by default, is a serious problem in my book. The previous version of Firefox didn't have the problem, as I have had that feature of Malwarebytes turned on for a good while. So what did you programmers change that "broke" it?