• A recent Microsoft fix will see a five-year-old problem between Mozilla Firefox and Windows Defender sorted.
• For many years users couldn’t find out why the Antimalware Service Executable from Defender was using so much CPU while Firefox was running.
• The fix will return around 75 percent of CPU performance to Firefox users on PC.

Windows Defender, the antimalware software included with every copy of Microsoft’s PC operating system has long been maligned for its poor performance. Recently, a five-year-old problem that the service was causing users of the Firefox browser has been smoothed over.

According to TechSpot, users have been struggling with performance issues with Firefox due to Windows Defender’s Antimalware Service Executable component (MsMpEng.exe), which began showing a strange high CPU usage when running simultaneously with Firefox.

“I noticed that for some time now most of the time Firefox is active, the Windows 10 built in ‘AntiMalware Service Executable’ is using well above 30 percent of my CPU,” wrote the user who reported the bug.

“This is considerably slowing me down and makes Firefox feel really slow.”

It seemed that the bug was only affecting Firefox, as it could not be replicated with Edge or other third-party browsers like Chrome. Mozilla developers finally discovered the root of the issue in March. Strangely, only while Firefox was running, the Windows Defender executable was making an unusually high number of calls to the OS kernel’s VirtualProtect function.

Basically, while the Mozilla browser was running, Windows Defender was running a lot of “useless computations,” Microsoft explains. In fact, one user pointed out that Windows Defender was stuck in an infinite loop of creating and deleting a series of temporary SQL files.

This caused Mozilla’s broswer and Windows Defender to suck up five times the CPU power than necessary, compared to the performance of other browsers. Luckily for Firefox users, Mozilla worked with Microsoft to find a solution to the problem.

The bug was finally closed on 4th April 2023 after a period of testing the fix. Mozilla says that the new update to Windows Defender, with the fix included, will provide a huge 75 percent improvement in performance while running the browser on Windows.

Microsoft recently stopped selling licenses for Windows 10, which often saw complaints from users during its tenure as the company’s leading PC OS, citing security problems, slow performance, errors in updates, common driver issues and more.

[Image – Rubaitul Azad on Unsplash]