From the 'tomAYto, tomAHto' files:

At the end of February I wrote about Mozilla developers calling for Firefox 3.1 to be renamed Firefox 3.5.  It's now official, so the next Firefox new version release will be Firefox 3.5.

Firefox 3.1 is currently at Beta 2 with a third Beta coming as soon as this week.

The reasons for moving the name from Firefox 3.1 to 3.5 are relatively simple. The release has taken more time than initially expected and the release contains more significant features than a simple x.1 release might indicate.

However, the jump to Firefox 3.5 doesn't mean that Mozilla is now adding more into what was known as Firefox 3.1.

"It's important to note that 3.5 represents a better labeling of our *current* scope, and not an indication that we intend to significantly increase this release's scope any further," Mozilla's Mike Shaver wrote in a mailing list posting. "Beta 3 will be the last milestone release with the 3.1 version number, and Firefox 3.5b4 will be the following one."

The version after Firefox 3.5 will now have the placeholder label of  Firefox 3.6, but that doesn't mean that is what that release will ultimately be called.

A jump from a x.1 to an x.5 release has historical precedent at Mozilla -- the same thing happened with the Firefox 1.1/1.5 release in 2005.

The general idea is that a bigger number signifies a bigger change to users. With a new JavaScript engine in place Firefox 3.1/3.5 is a big change.  Frankly I'm not sure why it wasn't labeled 3.5 (or perhaps even Firefox 4) earlier.

In a broader software context, major version changes imply a significant rewrite of a core component and sometimes a change in the underlying API compatibility.

In comparison to its competitors, Apple Safari is making the jumper from Safari 3.2 to Safari 4, based strongly on its new Nitro JavaScript engine. Microsoft is jumping from IE 7 to IE 8 with a long list of new features and as it ramps up its new Windows 7 operating system. Google Chrome stable is currently at the 1.x release with its dev-channel currently at 2.x

Like it or not, Firefox is in competition against other browsers and naming Firefox 3.5 is the right way to go, --  it implies something significant and based on my usage of Firefox 3.1 so far, it sure is one significant browser improvement.