Testing will be a top priority during that process, he added.

"We need *everyone* to help in testing," Sicore wrote. "Specifically: Do not disable Flash, Silverlight, or other major plug-ins as we need as many people testing these as possible. Windows users: We need to know if you are affected by hardware acceleration causing crashes or other issues."

Once it's done, however, "Firefox 4 is gonna kick ass," Sicore reminded the project's "tired and stressed" developers. "You should be fiercely proud of it."

'Do Not Track' Capabilities

Amid an ever-intensifying competition with Chrome, Internet Explorer and other Web browsers, Firefox 4's development has been watched with close scrutiny.