Why Firefox's strict JavaScript warnings are wrong

Firefox offers a strict JavaScript checking option. It can be enabled by either setting 'javascript.options.strict' to 'true' in about:config, or by enabling 'strict JavaScript warnings' in the Web developer extension. It sounds like a nice idea, to help you with your script debugging. However, before you get carried away and start trusting it, I must strongly discourage its use. It encourages, an

[murky-satyr]

plus more: trailing comma (only useful in cross-scripting with JScript / totally useless inside Firefox), silence on for-in bare-assignment (letting through the main cause of global leaks)...