Firefox only sucks for loading huge tables (like in phpmyadmin ;/). Boot up times are a little longer and memory usage is a lot bigger, but it's worth it. Also, I think IE 7.0 will be a stand alone product and not embedded into the OS, meaning, it'll probably have just the same effects as firefox.
Firefox's download manager sucks, IE doesn't have one.
Firefox likes to download pages sometimes instead of navigating them. I also get a lot of "document contains no data" popups constantly, and firefox does not like frames it seems. Could just be phpmyadmin though, but, firefox gets annoying inside it.
IE's annoyances greatly outweigh firefox's though, and I'm sure firefox will fix them soon. And teb page developer plugin is so sexy,

for yoshi for showing me it.
I need to find a sexy firefox skin.
QUOTE(chris)
Which is why you should ONLY support Firefox.
If IE 7.0 has it's own seperate priority code, away from standards and ie 6.0 even, I refuse to code for it. Either they

it up again EXACTLY like 6.0 or comply to standards fully. I'm not going to deal with three different styles for one page because of microsoft.
We'll see.