Rendering engine is not the issue. It's the JIT - firefox could publish a browser, it would just need to have interpreted javascript and it'd be useless.
Well, then it is good, I did not make a JIT (only XPath AST, not even bytecode)
Although I have been thinking about making a JIT. Building on for x86 is easy enough, but then it is useless for ARM. I would not want to build two JITs. Or four with 32/64-bits.
This is just wrong. Apple disallows apps that duplicate existing functionality, i.e. browsers. You can write whatever wack headless browser you want, and there are tons of frameworks for this exact purpose, too: All manner of methods to do network things without invoking Safari.
This is a jawbreaker of hyperbole around a chewy gum center of truth.