The link to download Firefox from the Android Market will not work on phones with incompatible hardware. You can check if your phone is compatible here:

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

Of the various LG Optimus phones, only the "Optimus Z" is compatible.

On some supported devices, a bug in the Market software prevents Firefox from showing up. This may be related to the fairly recent Android Market app update. If you go to Settings/Applications/Market and choose "Uninstall" you can uninstall the update, and then search for and install Firefox from the marketplace.

Or, if you have a supported phone, you can download the app directly from here:

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

Visit http://wap.mobiles24.com on your wap enabled handset you have to register for free first cus it will ask for a username and id

   Select Download by ID and enter 473854

   Click Download Item