Firefox has long been criticized for being resource-intensive compared to other browsers like Chrome and Edge. However, Mozilla has confirmed that the problem was not with the browser itself but a Windows Defender bug, which particularly affected Firefox.
After five years of waiting, it appears that the security tool’s issue has finally been addressed, and the CPU usage of Firefox for Windows is expected to drop significantly.
According to Yannis Juglaret, senior software engineer at Mozilla, Firefox’s culprit was a task named MsMpEng.exe, responsible for real-time protection that monitors web activity and eliminates malicious threats. The bug caused Firefox to call this service more frequently than comparable browsers, resulting in noticeable CPU spikes and reduced battery life.
The fix, which has “improved MsMpEng.exe’s CPU usage by ~75% when browsing in Firefox,” according to Juglaret, comes in the form of a patch for Windows Defender. The patch is currently rolling out to Windows 10 and 11 users and is expected to hit all users within the next week or two unless they block updates.
This is good news for Firefox users who have been frustrated by its high CPU usage, and it may help improve the browser’s reputation regarding resource management. It’s also a reminder of how complex software can be and how small bugs can significantly affect performance.