Johnathan Norman, Microsoft Edge Vulnerability Research Lead, said the idea behind the new Super Duper Secure Mode is to disable support for JIT (Just-In-Time) inside V8, the Edge browser's JavaScript engine. JIT, while unknown to most end-users, plays a crucial role in all of today's web browsers. JIT works by taking JavaScript and compiling it to machine code ahead of time. If the browser needs the code, it gains a significant speed boost. If it doesn't, the code is discarded.

JIT support in V8 is is a pain apparently and JIT-related security issues amounted to 45 percent of all V8 vulnerabilities in 2019.

More than half of the "in the wild" Chrome exploits rely on JIT-related bugs. Norman said that recent tests carried out by the Edge team have shown that despite its pivotal role in speeding up browsers in the early and mid-2010s, JIT is not a crucial feature anymore to Edge's performance.