There is *NO* new version of Firefox mobile right now available for windows mobile. Minimo is horrible and is very old. There will be a new one as people said before, called Fennec, and they recently showed off a pre-alpha build for symbian at
arstechnica but there are no other builds compiled except that pre-alpha for the symbian os. Even if there were, theres no installer, that's still in planning (at least for windows mobile). You could build it yourself, directions
here. Just a warning I tired building firefox once (I'm not a programmer though) and after 3-4 hours I gave up. You could always it a shot but unless you know coding or are familiar with compiling code its going to be hard... and probably not worth it honestly.. its really early in development.
It looks like its going to be at least 4 months - their own road map has them 2 months behind schedule (probably due to firefox 3 being delayed since its based on that) with an alpha at the end of August... so that makes it October/November - before you see a build you can just install and try... and then who knows truely how useable that will be... mozilla is great with the useability of its early testing builds but it'll still be an early alpha. There's all sorts of information
here about the project that is helpful. If anyone is interested in the UI mockups they're
here. Some are pretty nice.