Last month, Damon Sicore, Mozilla's director of platform engineering, said that the open-source company was shooting for a February release of the Firefox 4 final code. At that time, Sicore said 160 hard blockers remained, and that developers would "ideally finish the hard blockers by the beginning of February."

Legnitto also left open the door to yet another beta, which would delay a "release candidate" build even further.

"Beta 12 is currently planned to be the last beta (by definition due to not having any betaN hard blockers after it is created), but we still might need a beta 13 if issues found in beta 12 need beta coverage before a release candidate," he said Thursday.

Mozilla faces pressure from other top browsers. Microsoft, which shipped (IE9) Release Candidate (RC) last week, has sent out invitations to the press for a March 14 event at SXSW (South by Southwest Conferences and Festivals).

Microsoft, which mailed similar invitations in both September 2010 and January 2010 for events that later included roll-outs of IE9 Beta and IE9 RC, respectively, may use the SXSW conference to launch IE9's final build.