My goal is exactly how I stated it.
I wanted to ask if someone had Paste and Go with modified compatibility prerequisites, as Firefox 15 ignores the changes made in install.rdf. The extension works perfectly. The only problem is that guys at Mozilla Add-ons arbitrarily decided to take PaG 3 down when Firefox 4 was released what irritated the author making him take down all Firefox extensions down from his site.
You wasted your time trying to impose my goals with your "if"s.
I do not care about guys who make decision in Mozilla, as they intentionally choose to break the browser (as they did when they removed the statusbar and when they've hidden the RSS icon) so talking to them is a waste of time. Go to
https://input.mozilla.org/pl/feedback and you'll see that people mention the same things after every release yet Mozilla ignores them.
To anyone that also wants a Paste and Go in their Firefox 15: Use the "Disable Add-on Compatibility Checks" add on. Every function still works perfectly in Firefox 15.