In a letter posted to the nonprofit's Web site Thursday, the group said it would no longer develop features for its Mozilla Application Suite, otherwise known as Seamonkey, nor release a 1.8 version. But it will continue to provide developer support for its current 1.7 version.
Instead, the company will maintain focus on its Firefox browser and Thunderbird e-mail application, as it has since 2003, according to the letter.
"If we ship (Seamonkey) 1.8, we'll need to support that as well, and we just can't manage supporting that many versions as well as Firefox and Thunderbird releases," the letter stated.
The shift comes as Mozilla's Firefox has emerged as a viable rival to Microsoft's dominant Internet Explorer Web browsing software. The open-source software has put Microsoft on the defensive by garnering nearly 27 million downloads since its November final release. Thunderbird has received more than 4 million downloads.
Last month, Microsoft reversed itself and said it would release IE 7 with the next update of Windows XP. Previously, the company had said upgrades to IE would come only as part of the next major version of Windows, code-named Longhorn.
Still, Firefox's market share, which has increased rapidly overall, has begun to grow at ain the past month.