Mozilla's Firefox 4 is facing further delays, with several bugs still be resolved before the release of the Beta 12 version.
Five remain, including two in Firefox's hardware acceleration code that switches some browser page rendering to the graphics processor, according to reports from New Zealand.
Mozilla initially planned to release Firefox 4 in November 2010, but it announced in October that development would be finalised only early in 2011.
In January, Mozilla said it expected to have resolved the 160 remaining bugs by the beginning of February and to release the final beta later in the month.
Mozilla faces pressure from other top browsers, with Google releasing the latest version of Chrome on 3 February and Microsoft expected to release Internet Explorer 9 in mid-March after shipping the IE9 release candidate in Mid February.
In an attempt to step up the pace, Mozilla has laid out an ambitious schedule to release up to three upgrades in 2011.
Firefox currently accounts for 22.8% of all browsers in use, according to Web metrics company Net Applications.