About a month of development.

There has been a change to 4.0 and Gecko 2.0 on the trunk to indicate that there are major changes in the next release. So Firefox 4.0b1 if just the next test build (first beta in the row) following the last alpha release 3.7a5, obsoleting that version and you should update as soon as possible.

Be aware that it can (and probably will) break many extensions.

There are many extensions that no longer work in the latest Minefield nightly builds and Firefox 4.0b1 preview because of changes made to registering XPCOM components. See http://forums.mozillazine.org/viewtopic.php?f=23&t=1937759 ..... http://blog.mozilla.com/addons/2010/06/14/multiple-breaking-changes-are-coming-for-components-in-extensions/

I did not have a problem, just asked difference between Mozilla Developer 3.7a5 and FF4 beta 1. I didn't understand a word of the Geek_Speak in the reply. But the non-problem was been resolved when I received an update to Developer which turned it into FF 4.0b1. So, I guess the reply should have been: "They're the same after the forthcoming update."

Thanks, cor-el.

FWK