I've ran into a problem: given firefox extension released under GPL as shipped (.xpi files) has obscured .js files -- all formatting was removed. I've asked the upstream to provide proper source code, but so far he effectively refused to do that, although it seems to be a very simple operation to perform. For our discussion see http://z9.invisionfree.com/foxyproxy/index.php?showtopic=250 If I understood GPL license correctly, upstream author simply can't release anything under GPL if he doesn't provide sources. Whenever I've asked on mozilla's addons IRC I've got reply as "afaik he codes himself, and so if he writes on his page / in the package that it is gpl, you can use it under the gpl license" but I think that he/she is incorrect in his/her understanding of GPL.
Standard blunders of copyright no 1LICENCES DON'T APPLY TO AUTHORS (actually, that should read copyright holders, but often they're the same thing).
If the upstream author owns the copyright, and he gives you obfuscated source, then there's NOTHING you can do about it. I'd say it's actually even dangerous to de-obfuscate the code!
If you want to modify the code, de-obfuscate the bits you need, modify it, and then distribute as per GPL. IANAL, but you should be safe here, as you are distributing the original author's stuff "as is", and you are distributing the modified stuff in "a preferred form for modification", namely your preferred form because you're one of the people who modified it.
It's been mentioned "are you complying with the GPL if you distribute obfuscated source?". I'd say "yes", because you're distributing it unmodified as per what the original author gave you (I think that's legit as per the GPL - I think it says you can distribute "the unmodified source" without any further obligation).
Cheers, Wol -- Anthony W. Youngman - anthony@thewolery.demon.co.uk