Mozilla has announced the availability of Firefox 13, a new version of the open source Web browser. The update brings several major user interface changes, including a long-awaited refresh for the new tab page.

Mozilla Labs began experimenting with an improved design for the new tab page all the way back in 2009. At the time, the company used a browser add-on to prototype the interface. It aimed to build a useful and feature-rich start page without compromising the performance of opening a new tab.

The design that has finally landed in Firefox 13 is a simple grid of thumbnails, featuring sites that are frequently visited by the user or have been visited recently. The list of sites is populated by the same mechanism that powers Firefox’s AwesomeBar autocompletion system. The layout is similar to that of virtually every other major Web browser. It’s relatively unambitious, but it is sufficiently functional and doesn’t detract from the browser’s responsiveness.

When the user hovers their cursor over a tile in the new start page, icons will appear to let the user remove or pin the tile. These features behave identically to their Chrome equivalents. The user can also drag the tiles to reorder them as desired.

In addition to the updated new tab page, the browser’s start page also got a minor update. The browser’s default start page has historically been a Firefox-branded Google search prompt. The new version of the start page has a row of large icons at the bottom that provide convenient access to key browser features, such as history and bookmarks. Clicking these buttons will simply open the relevant dialog window.

In addition to the user interface improvements, Firefox 13 introduces a number of other minor improvements under the hood. The browser’s cycle collector, which works to free memory that is no longer needed, got some optimizations in Firefox 13. The tweaks should reduce its intrusiveness, avoiding some of the brief pauses that previously occurred during Firefox usage.

Another change that Mozilla’s developers have made to improve the browser’s responsiveness is a new on-demand tab loading feature. When the user restores a previous session, the browser will not automatically load the contents of every tab. Instead, it will load the contents of the tab that is currently active. The other tabs will be loaded as needed when they are made active. This feature will reduce the initial resource overhead of launching the browser and restoring a prior session.

Firefox 13 is also the first version of the browser to come with support for the SPDY network protocol by default. SPDY is an alternative to the traditional HTTP protocol that was originally proposed by Google. It offers some performance advantages over traditional HTTP, but it is currently used by only a few websites. Firefox will now use SPDY by default for websites like Google’s search engine where the protocol is supported.

Firefox 13 is another nice incremental update from Mozilla. The minor user interface changes offer a welcome improvement, though we would perhaps have liked to see something more innovative for the new tab page. The ongoing focus on boosting the browser’s responsiveness is also valuable work that will help to bolster the browser’s competitiveness. For more details about the release, you can refer to the official announcement. Firefox 13 is available for download from Mozilla’s website.