Mozilla won't fix 80% of Firefox 3.0's bugs, says Computerworld. This sounds like a lot, and that is probably true.
However, this is not exclusive to Firefox. All software, including Opera, is released with known bugs. If just about all bugs were to be fixed before release, new versions would be few and far between, leaving users waiting for other bugfixes for a very long time. At some point you simply have to draw the line, and release the new version. New versions will often include many important bugfixes and additions, and many people will benefit from these even if other bugs remain.
One should also realize that browsers are extremely complex programs. They have to handle text, images, audio, plugins, and so on. And they have to handle any strange kind of input from the user or strange code on Web pages.
In an ideal world, all bugs would have been fixed before release. Perhaps if the Web was ideal, with perfect code on websites and perfect input from the user, browsers would be easier to debug. But the real world is quite different. Browsers have to deal with the real Web, which means that there is a huge potential for bugs.
So before we jump on the "bash the buggy program" bandwagon, we should consider for a moment the hugely complex application that a Web browser is (whether it is Firefox, Opera or Internet Explorer), and the benefit new versions bring to a lot of people even if not all bugs have been fixed.
Even applications that may not be half as complex as a Web browser are released with known bugs. It might be right or it might be wrong, but it's how the industry works.
It's the real world.