For Firefox users:

[Hiro]

What theme do you use?
I use this:
https://addons.mozilla.org/en-US/firefox/addon/6269
And my homepage fits it perfectly:

[FullmetalGanon]

i have 3 beta 5 so i use the default

[ME##]

I use the default.

[Hiro]

i have 3 beta 5 so i use the default

Xp default. Still, that's nice. I was gonna get the beta but decided against it.

[Ezloﺕ]

i sometimes use firefox, and the theme is smb3

[superclucky]

ie7 firefox style

[Daddy]

I don't normally use Firefox on my computer but I just the default theme on the beta.

[Ricky]

Basically the same default Firefox theme but the images are green.

[Thyme]

Default. I used to have Winestripe (default Firefox 1 skin) because I didn't like the new default skin when it was updated to Firefox 2, but then I decided to finally try out the default and I haven't changed it back since.

[don't let's]

I use the  Vista-aero theme.

[JSLink]

Default, when I use it.

[Samus Aran]

Default when I use it...which hasn't been lately. Really, none of the themes that people make for it are that good...whereas I love the delicious "lix" theme for Opera.

I hate that SMB3 skin as well as redshift so much, and those seem to be the most popular.

[Wrench]

RedShift