Five years after it was first detected, Microsoft has finally fixed a bug which caused, while browsing the web using the Firefox browser, the CPU of the computers consumed much more than registered with other browsers, such as Chrome and Edge. The bug was related to the Windows Defender Anti-Malware Service executable process, MsMpEng.exe.
When this process was running at the same time as the browser, the problems started. Users complained that Defender was throttling the CPU and that Firefox would suddenly start to crash and become unresponsive, or very slow and lag.
It is the Mozilla developers themselves who have been in charge of Microsoft making the correction, and it is likely that they have done a good part of the necessary work to achieve it. Of course, they have corrected it in collaboration with Microsoft. But it was the Mozilla developers who discovered the source of the problem: when Firefox was running, MsMpEng.exe executed a very high number of calls to the Virtual Protect function of the operating system kernel while tracking Windows events (ETW).
VirtualProtect is a function in charge of changing «protection in a region of compromised pages in the virtual address space of the calling process“, as explained by Microsoft, and Defender was doing many”useless computing operations» for each event, whereas Firefox for its part generated many ETW events. A combination that led to CPU power usage five times that of other browsers.
According to what was published in the Mozilla message board dedicated to bugs, Bugzilla, and according to Microsoft, the bug fix «it will be distributed to all users as part of regular definition updates, which are packaged separately from operating system updates. This includes even Windows 7 and 8.1 users, although these platforms should not have experienced the performance issue with Firefox, mainly because the ETW events that caused it do not exist on them. older versions of Windows«.
This means that only users who have explicitly declined the installation of this update have not received the fix. Currently, already deployed to teams around the worldso Firefox users should have noticed better system performance when browsing the web.
Still, five years is too long to fix a bug, and the fact that Microsoft took so long to do so may lead one to think that it did so to benefit its browser, Edge. But apparently this delay may have had more to do with the fact that it is a problem of rather limited scope.
The Firefox browser is not the most popular, and is only used by 2.93% of users. It is not that Edge has much, yes, since only 4.64% of the total use it. But Chrome has almost 70% of the browser market share. By comparison, Firefox is used by a very small number of people.
