Good plan mate, I always build my software from source and definately feel I have a performance boost with firefox from doing so.
I'm not sure that you will find it all that easy to build with Visual Studio, but there's a guide
here for doing so. I don't know much about compiler optimisations with VC++ and they may not be available. Using GCC (windows port is called dgjpp) might be a better idea. You'll also need all of the usual GNU tools like Make etc. If you want I can give you the list of
configure options I used for me build.
Edit: Sorry, I misread, you wanted without MSVC++, then you'll probably wany Cygwin. The other alternative is to install a Linux distro with a cross-compiler installed (note you can still build for windows platforms in this way)