For the last five years, the Firefox browser has faced its competitors on Windows, mainly Chrome and Edge, at a clear disadvantage. A hard-to-detect bug in Microsoft Defender, the operating system’s security tool, forced the browser to consume far more resources than it needed to. Last March, Mozilla engineers -which is the organization that develops Firefox- finally found the problem. Defender’s real-time protection system, MsMpEng.exe, made too many requests to the operating system kernel, overloading the processor.
For some applications that need to use some of its functions, such as the well-known browser, this excess of requests resulted in much lower performance than expected. If the browser was running together with other applications, it could become temporarily blocked at certain times. The error led the program, at times, to consume up to five times more resources than it really needed. As much as the engineers tried to make the browser more efficient, they could not compensate for the higher consumption.
The issue had been known since 2018 and has been on Mozilla’s radar ever since with no apparent fix until a Mozilla developer, Yannis Juglaret, further documented the issue and managed to pique Microsoft’s interest.
The latest Windows Defender update, which began rolling out on April 4, corrects this bug and the results are remarkable. There is about a 75% improvement in processor usage. Now the development team is trying to detect if other antivirus and security programs might be having a similar effect on Firefox’s performance.
The browser is the fourth most used in the world, although far behind Chrome, which is used by almost 70% of users. According to StatCounter, which collects usage statistics from different browsers, Firefox is behind 2.9% of requests to web page servers, behind Safari (the browser installed by default on Macs) and Edge, the browser official from Microsoft, which uses the same engine as Chrome.
According to the criteria of The Trust Project
