Microsoft and Mozilla developers have worked together to resolve a compatibility issue between Windows Defender Antivirus and Firefox browsers that was first publicized about five years ago. This is an error in the Antimalware Service Executable (MsMpEng.exe) service of the antivirus program, which caused the CPU load to increase significantly when using Firefox.
A fix for this error was reportedly rolled out this week and will soon be available to all users. According to a Mozilla spokesman, after installing the update, the efficiency of the MsMpEng.exe process increases by 75% when using Firefox at the same time.
Microsoft previously acknowledged an issue with its proprietary antivirus online protection feature, which was consuming too much CPU time. The recent update helps reduce CPU usage, which should be noticeable when using Firefox. The browser itself suffered more from this bug as it generates 7x more Event Tracing for Windows events compared to competitors like Chrome or Edge. These events are processed by the VirtualProtect anti-virus function, which is why the processor load increases.
Although the latest update helps solve the problem, Mozilla developers plan to reduce the number of processes generated by Firefox. It should be noted that performance issues may occur when using Firefox and other VirtualProtect-enabled antivirus programs such as Norton products.