Mozilla foundation has already announced this around a month back that they’ll stop supporting Firefox Version 1.5 after 24th April. By support they mean that they’ll not release any more security upgrades for any version less than 2 and thus I’ll suggest you to upgrade your browser to Firefox version 2.0.3 (which is the latest version till this date.).
Almost each and every plugin, is now compatible with the latest version of Firefox and believe me, there is no point in using a plugin which is not updated regularly with the newest release of the browser. I’m sure that your security is much more important than your convenience.
So, one thing which I’ll say that UPGRADE WITH CONFIDENCE! (I’m sure IE 7 lovers actually love this line too!).
Links : Firefox