It will also benefit other users through lower power consumption. This will bring a nice performance bump for our users that have limited CPU resources, where MsMpEng.exe would sometimes consume 20%-30% CPU, and will now consume a single-digit percentage of CPU. We expect that on all these computers, MsMpEng.exe will consume around 75% less CPU than it did before when it is monitoring Firefox. Potential hang with moz:debuggerAddress capability set to true: After enabling the site-isolation feature in Firefox with geckodriver 0.32.1 some WebDriver clients like Selenium that use the Chrome DevTools Protocol (CDP) by default for logging events could trigger a hang in Firefoxs experimental CDP implementation. Nothing less, nothing more.įor Firefox this is particularly impactful because Firefox (not Defender!) relies a lot on VirtualProtect (which is monitored by MsMpEng.exe through ETW). The impact of this fix is that on all computers that rely on Microsoft Defender's Real-time Protection feature (which is enabled by default in Windows), MsMpEng.exe will consume much less CPU than before when monitoring the dynamic behavior of any program through ETW. You may read online that Defender was making too many calls to VirtualProtect, and that global CPU usage will now go down by 75% when browsing with Firefox. Step 2: A new window will open and begin looking for available updates. There has been some coverage in online news about the fix mentioned in comment 82. Step 1: Open the Firefox browser on your computer and then click on the browsers menu. Hence, after this fix, MsMpEng processor usage, when monitoring Firefox, should drop by around 75%. Jugarlet explains that the CPU usage is so high on Firefox due to the browser being heavily reliant on VirtualProtect, a virtual memory API, which in turn is monitored by Defender's Real-time Protection or MsMpEng.exe via Event Tracing for Windows (ETW). According to Juglaret, this is not the case as the 75% reduction percentage in CPU resource use is only taking into account the MsMpEng service and does not apply to global usage. Update: Mozilla engineer Yannis Juglaret, who isolated and worked on this bug, has shared additional context and details regarding the issue since some other news outlets were apparently sharing incorrect information that the global CPU usage would be reduced by 75%. Perhaps we will see such performance improvements in upcoming browser updates and it won't just be exclusive to Microsoft Defender alone. Interestingly, it has also been found that there is further scope of improvements to the processor usage in Firefox when compared to Chrome. Release date: Ap(Engine) / Ap(Platform).Security intelligence update version: 1.381.61.0.Here are details for the Defender update: Mpengine.dll version 0.4 was released on April 4, so the fix should be available for everybody now. Later on, Yannis Juglaret added that the recent Microsoft Defender March-2023 definition update (Platform. This includes even Windows 7 and 8.1 users, even though these platforms should not have had the performance issue with Firefox in the first place because the ETW events that cause it do not exist on these older versions of Windows. According to Microsoft, this will be deployed to all users as part of regular definition updates, which are packaged independently from OS updates.
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