If it seems like Mozilla just released a new version of Firefox, that's because they just did. Just back in March, as a matter of fact. If you're used to the long waits between Firefox releases — and inevitable schedule slips — those days are behind you. The Mozilla folks are now focusing on faster Firefox releases, with fewer features per release but a more steady cadence of updates.
If that sounds familiar, that's because Mozilla is taking a cue from Google Chrome (in terms of faster releases) and countless other open source projects that do time-based releases rather than feature-based releases.
The upshot of the time-based releases means that you'll see a steady stream of updates to Firefox — but not a slew of new features with each release.
User-Facing Changes in 5.0
It used to be that updating Firefox meant you'd see a lot of changes. The delta between Firefox 4.x and 5.0, though, is tiny — at least as far as user-facing changes are concerned.
This feature has been in the works prior to 5.0, but this is the first time it's popped up as a user-visible setting.
That it's in Firefox 5.0 is the good news. The bad news is that, well, it's optional for advertisers and other sites to honor the setting. So even if you have "Do Not Track" enabled, that doesn't necessarily mean that you won't actually be tracked. Sorry. Like the "do not call" list, it's probably going to take more than an HTTP header to actually dissuade many sites from tracking users — so don't let the setting lull you into a sense of anonymity.
Under the Hood
Let's look at some of the high-level new features for developers. First off, there's the CSS3 animations. They pretty much do what it says on the tin — animations let developers create animations using CSS rather than a technology like Flash. If you want a sample of what CSS animations can do, check out the Madmanimation which delivers an homage to the Mad Men opening animation using HTML and CSS animations. That's it. Note that it won't work in Firefox 4 or other browsers that don't support CSS3.
Firefox is no longer sending the "Keep-Alive" HTTP header. According to the Web developer blog for Mozilla, the header was redundant and formatted incorrectly as implemented in Firefox 4.x.
Another major change is that Firefox 5.0 only loads textures from the originating domain for WebGL content. Loading textures from other domains was seen as a potential security hole.
Those are the big changes, there's also a load of minor changes to how elements are handled and changes for compliance to standards or to be compatible with WebKit browsers.
Of Auroras, Betas, and Stable Releases
When the cycle began for Firefox 5, the Moz folks introduced three "channels" for Firefox. The stable release that we all know and love, a beta channel for users who want or need cutting edge features with a hint of stability, and the Aurora channel for adventurous users who are willing to trade stability for exposure to the newest goodies that may or may not make it into stable releases. Note that there's also the beta channel for mobile.
Originally the Firefox folks were going to have a "channel switcher" built into Firefox so users could easily select the channel that they received updates from. However, it was decided that this was unnecessary. Most of the users who wanted the Beta or Aurora channel were better served by running multiple releases of Firefox (for testing purposes) and the vast majority of Firefox users weren't a good target for Beta or Aurora.
Probably the biggest change in Firefox 5 is really the new release cycle. Before the end of 2011, the Mozilla folks plan to release Firefox 6 and 7. Firefox 6 will move into the beta channel on July 5, and Firefox 7 will move into Aurora on the same day — with Firefox 6.0 being released to the stable channel in August.
What does this mean for Linux distros that ship their own builds of Firefox? It depends on the distribution. The Mozilla folks have been in talks with distributors about backporting security patches and what will be considered acceptable changes to still carry the Firefox name. Red Hat Enterprise Linux and Ubuntu users will likely get the latest releases of Firefox through normal update channels rather than carrying forward old (such as 3.5.x) releases with patches.
Firefox 5.0 really isn't an urgent update if you are using the release that comes with your distro. If you're not having any issues with Firefox, it's not crucial to upgrade today — and the features in 5.0 really aren't so compelling that you will lose out by sticking with 4.x. However, if you're the adventurous type, I'd suggest skipping the 5.0 download and going straight to the Beta channel. I've been running Firefox development releases for a long, long time. Aside from the occasional extension that doesn't work with an update or hard-codes the version of Firefox it expects, I've run into remarkably few problems using Firefox development releases.
Already running Firefox 5.0? Let us know what you think!