Microsoft deigns to fix five-year-old Defender bug that slowed Firefox

After 5 years, Microsoft has addressed a bug successful its Windows Defender antivirus package that led to precocious CPU usage and wasted energy for users of Mozilla's Firefox web browser.

Back connected February 28, 2018, Markus Jaritz, a creation head for Firefox, revenge a bug report pinch Mozilla astir excessive CPU utilization arising from nan relationship of Firefox and Windows Defender.

"I noticed that for immoderate clip now astir of nan clip Firefox is active, nan Windows 10 built successful 'Antimalware Service Executable' is utilizing good supra 30 percent of my CPU, and is reference and penning random files successful 'Windows/Temp', each starting pinch 'etilqs_'.

"This is considerably slowing maine down and makes Firefox consciousness really slow."

Subsequent tests conducted by Jaritz indicated that Defender's Antimalware Service Executable (MsMpEng.exe, aliases Microsoft Malware Protection Engine) made much computational demands connected Firefox than connected Chrome.

Over nan adjacent fewer months, MsMpEng.exe became nan attraction of nan chat for creating and penning excessively galore etilqs files – temporary sqlite files. The problem was besides noted connected Reddit astir that clip and successful Microsoft's support forum wherever nan suggested workaround was disabling Windows Defender real-time protection.

In August of that year, Firefox technologist Marco Castelluccio observed that Microsoft was alert of nan rumor and said he had contacted nan Windows biz again arsenic a reminder that Firefox users were still having problems.

Then nothing. Years virtually passed and Firefox connected Windows continued frittering distant CPU cycles erstwhile Defender was progressive - until past month.

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In March, Yannis Juglaret, elder package technologist astatine Mozilla, looked into nan rumor and identified what was going on.

"There is simply a superior capacity rumor successful nan existent type of MsMpEng.exe, which I was capable to pinpoint utilizing nan WPR [Windows Performance Recorder] profiles from comment 78 and immoderate debugging," he wrote. "We person reported nan specifications to Microsoft, and they person acknowledged it.

"This performance issue makes calls to VirtualProtect (among different things) unreasonably costly connected Windows platforms erstwhile Windows Defender's Real-time Protection characteristic is progressive (the unreasonably costly computations execute successful nan MsMpEng.exe process)."

Microsoft, which touts its ain Chromium-based browser Edge to rival Firefox, patched nan bug successful its March 2023 Defender update, which was released connected April 4 for nan Defender motor and April 11 connected nan level arsenic a whole.

Redmond did not instantly respond to a petition to explicate why repairs took truthful long.

The hole intends that MsMpEng.exe will beryllium little demanding of CPU resources for monitoring programs successful real-time utilizing Event Tracing for Windows – for immoderate application.

"We expect that connected each these computers, MsMpEng.exe will devour astir 75 percent little CPU than it did earlier erstwhile it is monitoring Firefox," he wrote.

But that's only half nan conflict because Microsoft's bug was aggravated by Firefox creation decisions.

Juglaret successful consequent posts explains that Firefox was affected much than different applications because it makes dense usage of Windows' VirtualProtectEx function. So he opened a bug report to "Reduce nan CPU usage of antivirus package connected Windows erstwhile Firefox is running."

With immoderate luck, Mozilla engineers will beryllium capable to adjacent this bug study successful little than half a decade. ®