Firefox 3.5 includes some new features, functions and a few fixes thrown in to boot. Between its June 2009 release and September of that same year, more than 220 million copies of the new browser were downloaded worldwide [source: Mozilla]. In the first 24 hours of its release, Firefox 3.5 was being downloaded at a rate of 100 copies per second [source: Siegler].
The current generation of Firefox is built on the Gecko 1.9.1 rendering engine [source: Mozilla Developer Center]. A rendering engine is a program that interprets code and markup languages (such as HTML or XSL) and generates the image of the Web page you see in your Web browser. The Gecko 1.9.1 engine is faster than previous versions but it comes with a price. As Mozilla began to upgrade its engine, starting with Firefox 3 the browser isn't compatible with Windows 98 or earlier versions. It also won't work on versions of Mac OS X before version 10.3.
With earlier versions of Firefox, some people noticed their computers acting sluggish as they used the browser. It seemed that Firefox consumed more memory resources the longer it remained active, particularly if the user opened multiple tabs while browsing. Firefox had a memory leak.
Memory leaks aren't necessarily a serious problem -- most of the time, a simple reboot takes care of the issue. But having to reboot your computer multiple times whenever you sit down for an extended Web browsing break is pretty annoying. If you have a lot of applications running at the same time, your computer's processing speed might slow to a crawl. Patching the memory leaks became a top priority for Mozilla with Firefox 3.
The Firefox development team has several tools that help them measure and patch memory leaks. These tools have names like BloatView, Leaky and Trace Malloc. The developers used these tools to diagnose the problems in earlier Firefox builds [source: Mozilla]. In addition, the XPCOM cycle collector tool in Firefox 3.5 looks for unused memory to feed back to the computer [source: Mozilla].
Mozilla designed the browser to integrate as seamlessly as possible with different operating systems. Each version -- Windows, Mac and Linux -- has a look and style that complements the native operating system.
Next, we'll look at possible problems with Firefox.