I was thinking or hoping to be able to use the default theme in Fx3,
but in Fx3b5 on Vista 64 I find there's quite a few things not right,
which may or may not change before Fx3 release.

Looking at the Navigation toolbar buttons with large icons and small
icons, in comparison to the combined back/forward thingy I find both
the small and large icons could be a bit bigger. The small 'Home' icon
looks odd without a little door. When using small icons I'd prefer a
smaller version of the large combined back/forward thingy rather than
the different looking smaller one.

The 'Bookmark Star' on the Location Bar is yellow, which is fine, but
the "Display your bookmarks" icon looks out of place being a dark navy
book with a white star. It'd be better with a yellow star at least.

What's with all the blue? A shortage of, say, red or green paint? :-)
"Stop loading this page" "X" icon is blue! Red is for stop
"Close Tab" buttons on tabs when hovering is blue! Red is for close.
"Go to the address in the Location Bar" is blue! Green is for go, but
perhaps it is blue inline with the combined back/forward thingy?

And the worst thing is the tabs, imo, still dull and colourless like
the tab bar background, hard to see and absolutely no integration
afaics. Vista itself - Explorer, tabs on dialogs/options, IE7 even,
and other apps I use have colour on tabs, sometimes Vista's bluish
colours, which is better than the light greys that's still there.

I suppose it's easier to use another theme than try to change the tab
colours, tab close buttons colour, and icon sizes and colours?