Firefox 3 High CPU Use? Try This Fix.

In testing out Firefox 3.0 over the last several months I realized that when loading up a page in a foreground tab when two or more tabs were present, my single core CPU maxed out and loading slowed to a crawl making the browser unresponsive until I switched the tab into the background to let it finish loading. At that point, CPU usage returned to normal. As long as the tab that was loading remained in the background, the CPU never rose above an average of 20% max not counting the occasional spike or two from flash and script content.

Other folks were having these problems also which included high initial memory use for some as well so after much troubleshooting and constructive cursing I finally found the culprit that was causing this high CPU/memory use problem and I’m passing it on.

The fix is actually pretty simple and involves changing the state of “browser.cache.memory.enable” in Firefox’s “about:config“. Just follow the simple instructions under the image below:

• Type “about:config” into the FIrefox 3 RC1 location bar and tell it you’ll be careful (you’ll see what I mean).
• When the list of configuration options shows up, type “cache” without the quotes into the search bar as shown above. A list of all entries will appear with the word “cache” in them.
• Change the state of the “browser.cache.memory.enable” entry to “false” by double clicking on the entry itself. Make sure the state has indeed changed to “false”.
• Restart the browser and you’re done.

Firefox 3 should now run right along nice and fast no matter what tab is loading in the foreground and without the high CPU use as I saw before the change and apparently the memory problem is also fixed. Performance does not seem to be degraded at all by this change and speeds things up nicely.

If this fix helps anyone running Firefox 3.0.*, please leave a comment and let me know as I’m really curious if this works for others as well. You might also leave your two cents worth at the Mozillazine forum thread I started for this problem and if you really wish to make a difference you can post your findings or add your vote on the bug report I also filed.

Note (07/15/09): This fix is only for the Firefox 3.0.* series as Firefox 3.5 and above does not suffer from this problem. Also, not all Firefox 3.0.* users will experience this problem as it seems to be dependent on certain hardware configurations. Unfortunately, due to the numerous possible configurations of PC hardware (and yes, the acronym PC also includes Macs as PC simply stands for “Personal Computer”) it’s next to impossible to track down the exact cause.

Thanks!