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12/30/2005
02:05 PM
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The Trouble With Firefox

Users report high memory usage and freezes in version 1.5 of the open-source browser, but not everyone is having trouble

Mozilla Responds

Mozilla executives have expressed interest in our findings but don't appear fazed by the problems readers report. "We have more than 10 million downloads of Firefox 1.5, and the overwhelming feedback we've received ... has been positive," engineering VP Mike Schroepfer says. "We have heard some reports [of high memory use], and we're working through them now in hopes of a successful resolution. It's our goal to make Firefox users happy."

The next release of Firefox, version 1.5.0.1, is expected late this month or early February. The two main goals of that release are security and stability, Schroepfer says.


(click image for larger view)


One reader found Firefox 1.5 using a large amount of memory.
Other than the issue of high memory usage, Mozilla isn't working on any problems readers identified, Schroepfer and products VP Chris Beard say. So problems like high CPU usage, program freezes and lockups, and long pauses before a tab or the browser opens from hyperlink clicks in other applications might not be fixed in the next version of the program.

One reason Mozilla might not be seeing many reports on the program-freezing issue is that Firefox's built-in crash-reporting functionality, the Talkback 1.5 extension, doesn't report freezing incidents. It's tripped only by an actual Firefox crash, and in most cases, the freezing issue rights itself after a few minutes.

The high-memory-usage problem was evident in previous versions of Firefox. But some people report that it's worse in this version, with Firefox displacing as much as 250 to 500 Mbytes of physical and virtual memory on a Windows PC with 1 Gbyte of RAM. Of all the problems, this is the most commonly reported. It's unclear whether it's linked to high CPU usage and program freezing, but it's at least conceivable that it might be.

Possible Cause

This is purely speculation, but it's possible that Firefox 1.5's new Back and Forward button caching functionality--which speeds up the display of recently viewed Web pages--is contributing to the memory problem. There's a new small module in Firefox known as bfcache, which supports that performance improvement, Schroepfer says. Looking at the details about how much data bfcache stores, it doesn't appear that would be enough to cause the problems. The browser .sessionhistory.max_total _viewers setting in Firefox's about:config settings area, which is similar to the Windows Registry, stores only five pages on machines with 512 Mbytes of RAM, for example.

One Way To Curb Memory Spikes  
If Firefox 1.5 generates high memory numbers,
try this setting change:
 
>> Access about:config
by typing that exact phrase in the browser address bar and pressing Enter.

>> In about:config, look for this setting: browser.cache.memory.enable. Set its "Value" to "true," and follow these steps:

>> Right-click anywhere on the about:config window area and choose New and Integer from the pop-up menu.

>> The New Integer Value box will open. Type this setting name into the dialog box: browser.cache.memory.capacity
>> The Enter Integer Value box will open. The default setting is -1 and should preserve Firefox's existing mode of operation.

>> Mozilla provides more information about specific settings at kb.mozillazine.org/Browser.cache.
memory.capacity. For RAM sizes between 512 Mbytes and 1 Gbyte, start with 15000. For RAM sizes between 128 and 512 Mbytes, try 5000. If you have less than 128 Mbytes of RAM, that's probably the cause of your Firefox issues.
 
     
Many of those who reported they aren't having trouble wonder whether the people who are experiencing difficulty didn't properly uninstall previous versions (especially beta versions) of Firefox before installing Firefox 1.5. A related point is whether people reporting issues might not have poorly written Firefox extensions installed or extensions that might have been improperly tested for Firefox 1.5. Based on comments people have made in their E-mails, many are having trouble with cleanly installed versions of Firefox 1.5 that have no extensions or themes installed.

Memory Test

A substantial number of Firefox users have experienced the browser's penchant for using copious amounts of memory. We decided to test this by visiting some typical (but not excessively) graphics-rich Web sites, to see how that would affect memory usage. 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 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 were all JPEGs and none was more than 20 Kbytes. In fact, most of them were less than 15 Kbytes.

Instead of using a sterile, Safe-Mode Firefox 1.5 for this test, we decided to use a real-world setup. So we installed Adblock and Flashblock, turned on JavaScript, and turned off Java. That left us using two common extensions but not Flash or Java.

The screen shot below shows a custom Performance Monitor setup for the test, which graphs several key memory statistics for firefox .exe. The red lines show physical RAM accessible to Firefox, and the green lines show physical RAM accessible only to Firefox. The two lines move up in steps that 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. Although we repeatedly went back to only two open tabs and minimized Firefox to the task bar, Firefox almost never gave back a single megabyte of memory after the first 30 minutes or so.

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