There is a lot of cargo culting going on in this thread. There are 2 reasons to minify Javascript code:

1) Protect your intellectual property by obfuscating code

2) Make web pages load faster by reducing the size of the Javascript file(s) to transfer

Minifying an extension won't make it run faster since extensions are loaded from memory or disk, not from the network (ok, maybe it will be faster by a few nanoseconds?). It could make the initial download of the extension faster but it's only a one time download. Therefore, the only valid reason to minify an extension would be #1. However, it seems Opera is more concerned by user security (it's much easier for a backdoor to go undetected in minified code) than protecting the IP of extension developers.