Firefox 3.0 is the best web browser we've ever seen.

Of course, Firefox has been setting the standard for web browsers since it first appeared in 2004. At the time, Microsoft's Internet Explorer ruled the web, and it did a lousy job. But unless you were savvy enough to try alternatives such as Opera - or were still hoping that Netscape would get its act together - you were stuck with IE.

Firefox then was a breath of fresh air. It was everything that IE wasn't. It was secure and fast, and it supported extensions to transform the browser from a mere utility to the heart of the modern-day computing experience.

For a while, though, Firefox went into a decline. Mozilla kept adding features, but at the expense of memory, stability and performance. At the same time, Microsoft had finally been forced to improve Internet Explorer. Firefox was still better, but it was no longer that much better than IE 7.

With Firefox 3.0, however, Firefox is back on track.

Memory issues

One of the ways that Firefox 2.0 annoyed people was the way it handled memory. The longer their browsers were open, and the more pages were loaded, the more memory was used. The result for some users - especially those whose systems didn't have much memory to begin with - was that performance would drop to a crawl.

They also lost stability. With Firefox 2.x, we were averaging a complete Firefox failure - all browser windows either freezing or closing down - once every two days.

Firefox 2.x used different-sized chunks of memory. Then, as it constantly grabbed and released memory, its memory map began to look like a beaten-up jigsaw puzzle. Here a hole, there a troublesome spot where someone had torn off part of a piece to make it fit, and so on.

In addition, Firefox 2.0 kept full-size copies of images in memory. When you displayed a Jpeg or any of the other compressed picture formats, Firefox kept the full-size uncompressed images in memory even if you weren't currently looking at them. Since a single 100k image can eat up 1MB or more of memory, this old way of handling images can waste memory quickly.

Mozilla's engineers seem to have fixed that - or at least improved it - in Firefox 3.0. Now, if you're not looking at an image, it's been saved in memory in its original compressed format. They've also worked on the memory map issue.

Firefox 3.0 is now using expiration policies in its memory caches. The developers' thinking is that if you haven't retrieved a previously viewed page in half an hour or so, the savings in memory by dropping the page from your cache are more important than the small possibility your page will load faster if you retrieve the stale document.

The result is that, regardless of any other improvements, Firefox 3.0 is faster and more stable than its predecessor. We found that, on average, opening and closing tabs on Firefox 2.0.0.14 used up about 5 percent more RAM per browser tabbing session compared with Firefox 3.0. And in the weeks we've been running Firefox 3.0 on multiple systems on the same exact same PCs doing the same work as we were doing with Firefox 2.x, we haven't seen a single freeze-up.

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