is it right for firefox ?

Well, there's the argument that firefox is a third party, google has no control over them, and they don't own google. In other words, they aren't using one product to try and promote another one.
And IMO, they should have worded their complain differently. The issue isn't that search defaults to msn; it already does that in the current version of ie if you just type in a search term and press enter. The main problem, as I see it, is that micro$oft provides no easy way for the user to change their search engine (they have to click "change engine", which launches a webpage, then find your preferred engine, and select it...not easy for the average user). On the other hand, in Firefox, there's an icon making it clear which engine you're using. click on that, and you get a dropdown list including google's competitors. That's the difference, and that's what they should have focused their argument on. The "not fair to set as default" is a weak argument.

I wonder why Google even tried...