[slau]

I'd love to be able to modify JS at runtime on random websites. Too often there's a bug, or a "feature" that prevents me from using a service, that I could fix by removing an event or something in the JS code.

[holowoodman]

That's what development tools are for. Or Greasemonkey/Violentmonkey.

[slau]

As far as I know neither Firefox nor Chrome allow you to modify the JS prior to execution without a plugin. You can run random JS, sure, but you can’t monkeypatch.