Mozilla Suite : FAQs : GMail
From MozillaZine Knowledge Base
How do I use Mozilla with GMail, Yahoo and/or HotMail?
Mozilla Mail does not support GMail, Yahoo or HotMail as default. You need third-party solutions to be able to use Mozilla Mail with their services. However, you can use Mozilla browser with GMail (and Hotmail and Yahoo mail too).
Take a look here:
One might also consider employing the following extension, that affords similar functionality: