As Mozilla finally nears completion of the next generation of its popular open-source browser, the beta version of Firefox 4 begins to solidify into its final form. In the latest Firefox 4 beta, the browser focuses on faster start-up times brought by making improvements elsewhere in the code.

Firefox 4 beta 9 (top) moves the tab bar to the same level as the menu button. In Firefox 4 beta 8 (bottom), it was on a separate row.

Available for Windows, Mac, and Linux, Firefox 4 beta 9 debuts new under-the-hood code for bookmarking and history. You won't see any interface changes to those features, although they do load faster now. As a consequence of those snappier load times, the browser itself will start faster, the company said in a blog post. When comparing the averages of three "cold boot" runs, each of which started from the computer turned off and ended with fully loading 11 JavaScript-intensive pages, between Firefox 4 beta 9 and the previous beta 8, Firefox 4 beta 9 came in nearly 10 seconds faster. Firefox 4 beta 8 averaged 41.04 seconds until all the pages had loaded, while Firefox 4 beta 9 averaged 32.48 seconds.

Another change in Firefox 4 beta 9 brings code improvements to how complex animations are rendered, and they are expected to be much smoother as a result. The changes create more than one heap for garbage data in Firefox, which will prevent multiple JavaScript objects from multiple tabs from slowing the browser down. Another consequence of the change is that JavaScript elements in memory will be shielded from each other, so if one crashes, it's less likely to take others down with it.

A new database standard has also debuted in the latest Firefox beta. Called IndexedDB, the technology replaces Web SQL and has been extensively used for managing user data in offline situations.

A final and minor change to Firefox 4 beta 9 brings the tab bar up a few pixels, so it now sits on the same row as the Firefox menu button. The top of the browser now looks extremely similar to Opera 11 and Internet Explorer 9 beta. The full and technical change log for Firefox 4 beta 9 is available here.