Yes, but execute disable is not the same as execute only. AFAIK there's no way to prevent executable pages from being readable using only the i386/amd64 page table.
No. Isolation has always been a security feature, not a reliability feature.
Consider that local privilege escalations are generally (and I'd say correctly) treated as critical severity issues. Any general purpose process memory read-isolation leak is a quick route to a local privilege escalation, so how could isolation be anything other than a security feature? In its absence, you might as well run everything as root and there would be no point whatsoever to caring about privilege escalations.
It's not. They're just using the term as a synonym for "rewrite". There's no documentation of any actual IP isolation in the linked article. They just want people to know it's new and not based on the existing LLVM or Linux runtimes.
The PROT_WRITE tweak is interesting. Being able to enforce a bit of Write XOR Execute behavior in Write OR Execute arenas is nifty. It took this change for me to read into W^X and exactly what it entailed because my naive understanding was that the new no-syscall-from-writeable-page behavior would be almost identical in effect to the strict W^X behavior.
I believe the 'First-party isolation' feature does this, but you need to enable it from about:config, and even then, I'm not sure if it is complete or bug-free.
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