Firefox might not appear in the Market because it is not compatible with your hardware. You can check if your phone is supported here:

https://wiki.mozilla.org/Mobile/Platforms/Android

On some supported devices, a bug prevents Firefox from appearing in the Market. This may be related to the recent Market update. You can go to Settings/Applications and uninstall the Market update, then find and install Firefox.

Or, if you have a compatible device, you can download the app directly from here:

http://ftp.mozilla.org/pub/mozilla.org/mobile/releases/4.0b3/android-r7/multi/

(Note: To download the app directly for an AT&T phone, you will have to search for instructions on "sideloading" the APK file, since AT&T has removed the option to install from non-Market sources.)

Im not downloading from the market... Im downloading straight from the firefox website... The app for firefox is not even in the old market.... And i have the samsung vibrant, so i know its compatible

Thanks for the link to download