Firefox 3.5 Release Candidate (RC) was the first milestone since Beta 4, which Mozilla released in late April, and the second to carry the '3.5' label. The upgrade was originally called Firefox 3.1, but the company decided in March that it had added enough new features to justify the larger bump in number from last summer's Firefox 3.0.
Mozilla has had to delay Firefox 3.5 RC several times because of lingering bugs that defied fixing. Earlier plans had envisioned its release in the first week of June.
In fact, Mozilla took a pair of unusual steps this month as it neared Friday's delivery of Firefox 3.5 RC. It issued an interim build two weeks ago that it described as a nearly-finished RC, but offered the "Preview" only to the 800,000 daily users of Beta 4.
Last week, it repeated the move by pushing another update to the same 800,000.
"As soon as QA performs basic...tests on the milestone, we'll ship the partial updates to our existing beta-channel users," explained Mike Beltzner, the director of Firefox, in a message posted to a Mozilla developer forum on Wednesday. "Then, while our quality assurance team finishes more in-depth functional testing, our large beta audience will be helping us by using the builds across the breadth of the Web. We'll get wider feedback earlier, giving us even more confidence before we declare a milestone as final."
Mozilla issued the first such build last Tuesday, calling it "rc1build2," said Beltzner, because it was "the first revision of the release candidate for which we'll ship updates, and it required two build attempts,"
The new process is somewhat akin to what Google has been using with its own Chrome browser. Google, for instance, maintains a trio of 'channels' -- developer, beta and stable -- each updated automatically as new builds are available, each channel more stable, and thus offering older versions, than the one before. Although Mozilla also uses a similar multi-channel approach, this is the first time it has offered incremental, partially-tested code to large numbers of users.
Beltzner said that the final version's target date remains the end of this month, although to ship Firefox 3.5 by then will require a faster pace than last year's delivery of Firefox 3.0. If Mozilla decides to roll out a second release candidate, it will likely miss its deadline.
Firefox currently accounts for 22.5% of the browser market, according to Web metrics company Net Applications' May data. It faces renewed competition on almost every front, including Microsoft with its Internet Explorer 8, Google's Chrome browser, Opera Software's Opera and Apple's Safari 4, which launched earlier this month.
Users running Firefox 3.5 Beta 4 or one of the incremental release candidate builds should receive an offer to update to the Firefox 3.5 RC. They can also choose "Check for Updates" under the "Help" menu to do a manual update.
Others can download the release candidate from the Mozilla site.