As recently as September, Mozilla was planning to deliver the final of Firefox 3.6 by early November. Subsequently, Mozilla began using a by-year's-end window to describe its release plans for Firefox 3.6.

Such delays are not unusual. Last year, for example, Mozilla originally shot for a late-2008 release of Firefox 3.5, but eventually to mid-2009 in order to add features and quash troublesome bugs in the then-new TraceMonkey.

Firefox controls about 25% of the global browser market, according to the most recent data from U.S.-based metrics company Net Applications. Over the past week, however, as users tried out 's Chrome, which made beta for Mac and on Dec. 8.

can be downloaded from Mozilla's Web site for Windows, Mac and Linux. People using an earlier preview of Firefox 3.6 should see upgrade notices shortly if they haven't already.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld . Follow Gregg on Twitter @gkeizer , send e-mail at gkeizer@ix.netcom.com or subscribe to Gregg's RSS feed .