Previously we've already heard that theme changes for Firefox were dropped from 3.7 altogether and are purely being focused for the 4.0 release. But now it seems that there's more going on...

Once Firefox 3.6 is released sometime this month (hopefully) there may not be a successor this year. Yup, Firefox 3.7 might be canned, and although we might see the first beta's of Firefox 4.0 at the end of this year, the final release is probably coming in the beginning of 2011, leaving a big gap, or not?

Well, apparently Mozilla has the plan to introduce some of the Firefox 3.7 features into 3.6. For instance we'll see the full scale of Electrolysis (separate processes for plug-ins and tabs, like Chrome) in 4.0, but over the course of time this year we'll get minor feature updates for 3.6 of which one is plug-in process isolation (like Safari 4 on Snow Leopard). Risky changes that might affect the user experience, such as a new theme, or other GUI changes are not part of these minor updates though.

Whether it will pay off remains to be seen, but it definitely seems like a better way to have regular releases especially with the aggressive release cycle that Chrome has. With the automated test system and branches for small projects (that integrate into the main branch) they hope to hold a tight enough grip, to not cause major regressions.

Update: Corrected story to indicate this is the most likely plan to be executed, see for more details the response from Mike Beltzner.