"Firefox 3.0 is not yet officially out the door but Mozilla
developers already have a plan--and a timeline--for Firefox 3.1.
The draft plan--as it is currently being floated on the Mozilla
developer lists--is for Firefox 3.1 to be released within six
months of the release of Firefox 3. Considering that the final
Firefox 3 is likely within a matter of weeks that would mean we'll
see Firefox 3.1 in 2008.
"The release of Firefox 3.1 will also mark the likely end of
life for support of the current Firefox 2.x browsers. The plan (as
it has been since the release of Firefox 1.5) is to have
security/stability updates once every two months or so, until the
next 'feature' release--which is Firefox 3.1..."