Firefox 1.5 has been out since November 29, 2005, and has garnered glowing reviews around the Internet. This is not one of them. In fact, I recommend holding off, at least temporarily, on installing Firefox 1.5.

I've installed and used Firefox 1.5 through the betas, and had no trouble, but somewhere early in the Release Candidates I began to encounter problems. And I'm beginning to learn that I might not be alone in that. I can't speak with authority that a large number of Firefox users are having issues with Firefox 1.5; I am, though, hearing sufficient reports about trouble to be cautious. (You can find a report on readers' responses to this article, and Mozilla's response as well, at Firefox 1.5 Stability Problems? Readers And Mozilla Respond).

The issues people are reporting to me are highly varied. Some of the more dramatic problems have included damaged Firefox profiles and loss of right-button context menus, but the more common issues by far have to do with CPU and/or memory usage.

Problems With Memory
Matt McKenzie, Editor of the Linux Pipeline, recently sent me a screenshot that showed Firefox 1.5's main process (firefox.exe) using 398,108K physical memory and 405,540K virtual memory — way more than is comfortable or necessary. And the number, he said, was rising while he was sitting there. On the other hand, on my system, a quick check showed Firefox 1.5 using about 27,000K on first launch, and between 50,000K and 60,000K after a couple of hours of hard use. That level of memory use is within bounds. (By comparison, IE6 used only 13,000K after initial launch on the same machine in the same session.)

Some Firefox 1.5 users have reported huge memory hits. (Click to enlarge image.)

But even though I'm not experiencing the same issues, I don't think Matt McKenzie's problems are isolated. I've personally seen 100 percent CPU spikes when Firefox is laboring at something, a symptom that might be related.

In addition, several readers have written with concerns about memory leaks in Firefox 1.0.x and 1.5. A memory leak is an errant programmatic process that over time can gradually eat away at system resources. In worst-case scenarios, a memory leak could cause an application to become unstable. Under all Win 9.x versions of Windows, an application memory leak can also cause the operating system to become unstable.

The truth is, all but the very simplest of programs have memory leaks. But some programs are much worse than others. In the 1990s, I did a series of articles on Netscape 2.x because it was plagued with problems, including memory leaks. So this is not without precedent.