Firefox full chain exploit for CVE-2019-11708 + CVE-2019-9810

Targets Firefox 66.0 x64 instead of a custom build of Firefox like in the original PoC.

Changes from the original PoC:

Moved away from the use of "BigInt" since it was an test feature at the time and was not enabled by default.
Adjusted offsets for Release build 66.0
Removed unused code
Executes after the OnLoad event fires.