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.)

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. Counting The Glitches
It doesn't help that I'm personally seeing persistent issues with Firefox 1.5 myself. By and large, the problems I've had fall into two camps:

In addition, PDFs are now a total adventure. Sometimes they work, sometimes they never finish loading. And I'm using the latest version of the Adobe Acrobat Reader.

Not All Bad News
This is not to say that Firefox 1.5 isn't a good or worthy application. The new feature set is pretty modest overall, but all of the additions are good ones. The best new features are the automatic browser-updating functionality and the ability to check for multiple extension updates simultaneously. The new browser also automatically disables, but leaves installed, any extensions that don't explicitly support it.

Other new features include the ability to drag-and-drop reorder tabs, a significant reworking of the Options user interface (although the actual configuration settings aren't that different), and you can one-click delete your private data (such as user names and passwords) if you think you're being attacked by a phishing scam. For a good visual summary of the browser, you can read our first look at Firefox 1.5 Beta 1. Perhaps the most important change since that article was written is that many more Firefox extensions have added support for Firefox 1.5. For more on my favorite extensions and tweaks — and whether they support Firefox 1.5 — see my recently updated Best Firefox Extensions and Customizing Tips site.

Harsh Criticism?
I'm a confirmed Firefox user, an ardent supporter of this excellent open-source Web browser. But that doesn't mean I'm a lemming. Right now I think you might be better off hanging back if you haven't installed this puppy yet — especially if Firefox is your main browser. There are enough issues people are contending with that — who needs the extra headache? It'll probably all get sorted out. At least for the time being, keep using Firefox 1.0.7, or one of the other Web browsing options.

If you are already running Firefox 1.5 (or have decided not to take my advice to hold off), please write me with details about how well Firefox 1.5 is working for you. Is it ready for prime time? What do you think?