Mozilla has added a fourth beta of its latest web borwser, Firefox 3.6, into its schedule, but maintains the final code will be still be made available by the end of the year.
Mozilla released Firefox 3.6 Beta 4 last week after developers decided that the browser upgrade needed further testing before moving on to a release candidate.
"Due to the excellent work on knocking down the Firefox 3.6 Beta topcrash list, we've decided that it would be worthwhile to ship another beta update to our close to half million testers to confirm our expectations," Mike Beltzner, the director of Firefox, said in a message posted to the Mozilla developers planning forum.
"We'd also like to get as much feedback as possible on the more than 140 fixes we've made since we shipped the update last week."
Mozilla shipped Firefox 3.6 Beta 3 on November 17.
In a follow-up post on the Mozilla developers blog, Beltzner bragged that about 70 percent of the available Firefox add-ons - a crucial component to the open-source browser's success in grabbing market share from Microsoft's Internet Explorer - had been upgraded so that they were compatible with Firefox 3.6.
The insertion of the fourth beta has pushed back the delivery of a Firefox 3.6 release candidate, as well as the final code, although Mozilla maintained that it would still wrap up the latter before 2010 begins.
"Closing on blockers in order to deliver a release candidate build this week," Mozilla said.
"Still aiming to be ready to ship in late December."
As recently as September, Mozilla was shooting to deliver the final of Firefox 3.6 by early November. Subsequently, Mozilla began using a before-the-end-of-the-year window to describe its release plans for Firefox 3.6.
Delays are not unusual for Mozilla, or for other software developers.
Mozilla has cast Firefox 3.6, and its follow-on 3.7, as minor upgrades driven by a faster-paced development cycle . Firefox 3.7 is to appear in the first half of 2010.
Firefox accounted for 24.7 percent of all browsers used during November, according to data from web metrics company Net Applications.
Firefox 3.6 Beta 4 can be downloaded from Mozilla's website. People using an earlier preview of Firefox 3.6 should have been automatically upgraded to the newest beta.
See also: Firefox 3.6 to block sneaky add-ons