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Firefox 1.5 Stability Problems? Readers And Mozilla Respond

Firefox users wrote to us detailing their problems with the browser, and we asked Mozilla for some answers.

Pushing The Memory Envelope
This story is not about causes -- it's about symptoms. In our earlier story we speculated that altered JavaScript support and a possible application memory leak could be causing some of the problems. However, we can't definitively point to changes in JavaScript support or memory leaks as the cause of the problems some people are having with Firefox 1.5, and after reading 450 e-mails, both of those possible causes seem less likely to us.

Many of those who reported they aren't having trouble also wondered whether the people who are experiencing difficulty didn't properly uninstall previous versions (especially beta versions) of Firefox before they installed Firefox 1.5. A related point is whether people reporting issues might not have poorly written Firefox extensions installed, or Firefox extensions that might have been improperly tested for Firefox 1.5. These are legitimate questions -- although, based on statements people have made in their e-mails, many are having trouble with cleanly installed versions of Firefox 1.5 that had no extensions or themes installed.


In This Article

Reports Of Problems

Some Examples From Readers

Memory, CPU, And Stability Woes

Mozilla's Response

Can Bfcache Be The Problem?

Pushing The Memory Envelope

Whose Fault?

What is patently clear is that a substantial number of Firefox users have personally experienced Firefox's penchant for using copious amounts of memory. We decided to push a typical Firefox configuration by visiting some typical (but not excessively) graphics-rich Web sites, to see how that would affect memory usage. The goal was to reproduce the memory-management problems seen previously.

Less Tabs, Same Memory
We ran Firefox 1.5 in Windows XP in a consistent pattern over the course of a couple of hours. We opened new pages in tabs until five to seven tabs were open, closed all but two of the tabs, and then waited a few minutes to repeat the process.

We opened a total of about 80 pages in tabs this way. At all times, one tab was a Weather Underground page opened to the San Francisco weather radar, which is a looping series of six optimized JPEGs. The other tabs were opened to pages on the site with an archive of nature and weather photos. These photos are nothing special; they're all JPEGs and none was more than 20KB. In fact, most of the photos were less than 15KB.

Instead of using a sterile, Safe-Mode Firefox 1.5 for this test, we decided to use a "real world" setup. As a result, Adblock and Flashblock were installed, JavaScript was turned on, and Java was turned off. So while there were two very common extensions in use here, there was no Flash and no Java.



The red and green lines show physical RAM accessible to Firefox. The jumps match newly opened tabs, and the level areas match closed tabs. No memory was returned. (Click for complete image.)

The screen shot above shows a custom Performance Monitor setup, which graphs several key memory statistics for firefox.exe. The most interesting elements are the red lines, which show physical RAM accessible to Firefox, and the green lines, which show physical RAM accessible only to Firefox.

The two lines move up in steps; the jumps match the points when we opened series of new tabs, and the level areas match times when we closed the tabs and then waited before opening a new set. Notice that, although we repeatedly closed back to two open tabs and minimized Firefox to the taskbar, Firefox almost never gave back a single MB of memory after the first 30 minutes or so.

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