Oh and yes, javascript:alert(debug) gave me true (though I had to clear my browsers cash with CTRL+SHIFT+DEL i FF).

Setting breakpoints and having it break on them on subsequent run works for me in Firefox 4.0b11 with Firebug 1.7a11 (except when Firebug's script debugging is entirely broken by some bug that sometimes makes it claim there's no JavaScript on the page).

Seems ok in Opera 11.01 too. (Tested both on Mac OS X 10.6.6) Is there a very specific piece of code where the breakpoints don't work?

The only way to break on a script for me was to insert a "debugger" statement. So I guess it's not that bad as I originally thought.

Loading any scripts sources loaded with importScript still doesn't work for me in: Mozilla/5.0 (Windows; U; Windows NT 6.1; pl; rv:1.9.2.13) Gecko/20101203 Firefox/3.6.13 (.NET CLR 3.5.30729).

Note that scripts from bits load fine. I'll try to ask someone from FB team to comment.

(In reply to comment #3)

Seems ok in Opera 11.01 too. (Tested both on Mac OS X 10.6.6) Is there a very
specific piece of code where the breakpoints don't work?

Hm... I was unable to set any breakpoint yesterday at MediaWiki:Vector4monobookies.js in Opera/9.80 (Windows NT 6.1; U; pl) Presto/2.7.62 Version/11.01. Strangely it works now. Maybe it works because the script was altered now and it was something with cache? I'll try to test more thoroughly later today.

Not sure what changed but it started to work now. Opera thing must have been just a cache thing.

FB thing is a bit strange. FB shows me a lot of different scripts. The first ones that appear on the list are those that say "Failed to load source for sourceFile scriptTag". Now that I've checked it seems more likely to be a problem with FB anyway.