Mozilla said it hopes to release its second beta version of Firefox 4 "on or about July 22," bringing Mac users a major new user interface that the first beta enabled by default only on Windows.
That feature, called tabs on top, follows the look of Google Chrome and Opera, in which tabs get top billing over the address bar. It's not revolutionary, but it's hard to change the habits of software used by hundreds of millions of people, so Mozilla has made it easy to switch off and has been taking pains to explain its tab rationale.
"Recently modern browsers have been transitioning to placing tops on top, and that decision isn't arbitrary, it isn't about fashion," said Firefox user interface designer Alex Faaborg. "The change to placing tabs on top isn't about one browser versus another browser, it's about the evolution of the Web as a platform."
Not everybody sees things the same way. Apple tried a tabs-on-top approach with the Safari 4 beta more than a year ago, but moved them back to a subordinate position for the final release. It kept that design for Safari 5, too.
According to Mozilla's Firefox planning meeting agenda, also coming in the Firefox 4 second beta are CSS transitions, a newer feature of the Cascading Style Sheets technology used for Web page formatting. Transitions enable visually elaborate changes in a Web page's state, for example, making photos in a slideshow flip out of the way as a person moves from one image to the next.
CSS transitions enable the spiraling arrival and departure of the slides in a demonstration by Mozilla's Paul Rouget at last week's Mozilla Summit 2010.