As fo3nix said, there have been some serious bugs in Firefox which have been fixed (latest version 1.04 has them fixed). There will no doubt be bugs in future versions too.
As for point 2, some of the blame lies at MS's doorstep abusing the prominent position of IE and adding proprietary functionality to industry standards. Some developers use this added functionality to make their life easier and the website much more interactive. Unfortunately at the expense of compatability with other browsers.