Firefox 5 will be very similar in appearance with Firefox 4, most of the changes are behind the scenes. For an overview of the changes in Firefox 5 see https://wiki.mozilla.org/Features/Release_Tracking

Mozilla is moving into a rapid release system similar to that used by Google Chrome. Firefox 5 is not a service pack for Firefox 4, though it will replace Firefox 4. About 3 months later Firefox 5 will be replaced by Firefox 6.

Unlike the update from Firefox 3.6 to Firefox 4, there will not be major changes and I anticipate that most add-ons that work in Firefox 4 will work in Firefox 5. Add-on that are hosted on the official add-ons site will be checked by Mozilla prior to the release of Firefox 5 to confirm that they are compatible.

Rapid release? So that explains the *. Whatever happened to testing first, and only then releasing? Are you guys aware that you messed up the computers of more than 155 million (155,000,000) people with your "rapid release" *? Managers took over from techies at your company didn't they?

And by the way. I do not use google and blocked all google websites in FF. Please do not think that you are smart by replacing ff by chrome.

Edited for language - https://support.mozilla.com/kb/Forum+and+chat+rules+and+guidelines

Only changes that have been backed for 6 weeks in the Nightly builds are moved to Aurora.

• https://developer.mozilla.org/devnews/index.php/2011/04/07/new-development-channels-and-repositories-for-rapid-releases

Extensive testing of Firefox hasn't changed. We still have extensive automated tests performed as part of a "continuous integration continuous integration" process, and these tests are constantly improved in response to both added features and fixed bugs to help make sure that Firefox does what it's supposed to do.

We also have an open testing, development, and bug reporting process, which also help to make sure bugs get squashed as early as possible. Dozens of Mozilla staff and community members are dedicated just to quality assurance, and hundreds of thousands if not more participate in the nightly, aurora, and beta channels, which offer members of the public early access to what we are working on - and the chance to catch bugs early.

Check out http://quality.mozilla.org for a glimpse into the testing process. Rapid release really doesn't change much for testing - testing is going to be as thorough if not more so than it has been before.

HolyMan, The Firefox 4.0 was not even remotely a rapid release as it was originally scheduled for release back in August last year early on in development.

They did do testing with Fx 4.0 as besides the daily nightlies, there were five Alpha's, twelve Beta's, and two RC's before release.

Firefox 5.0 will be more like a minor major release as if it was a Firefox 4.1 release and perhaps a improved 4.0.*

It seems like Mozilla is mixing up "rapid release cycle" with "major upgrade release". A rapid release cycle doesn't require a major upgrade every cycle. It would just be nice to have rapid *minor* releases within the major version number, then upgrade the major version number every year or so. This seems like more of a marketing ploy than anything, and it's messing with web development compatibility.

Glad to see that the changes in Firefox 5 are 'behind the scenes'. Hopefully they will address the speed and stability issues that have made using Firefox 4 such an annoying and frustrating experience?

I agree with dhinged. This descision to use the major version and rapid releases to work together seems ludicrous to me. Also, it seems to me that the entire system for plugin compatiblity control has been shot in the head as the upgrade to version 5.0 was a debacle for plugins. Over half the plugins I depend on failed to operate after the upgrade. So I do not think FireFox 5 is backwards compatible at all.