https://connect.mozilla.org/t5/discussions/resistfingerprinting-inadvertently-increases-uniqueness-dnt-auto/m-p/138870#M56435 <P>Hello Mozilla,<BR /><BR />I'd like to share two findings about Firefox's fingerprinting resistance&nbsp;<BR />(resistFingerprinting) that I believe are working against their own goal&nbsp;<BR />of making users less unique, rather than more.<BR /><BR />1. Enhanced Tracking Protection automatically enables the Do Not Track&nbsp;<BR />header, and this cannot be disabled without also disabling tracking&nbsp;<BR />protection itself. According to my testing on EFF's "Cover Your Tracks"&nbsp;<BR />tool, sending DNT actually adds around 1.9 bits of identifying&nbsp;<BR />information, because relatively few browsers send it today, making it&nbsp;<BR />counterproductive to the goal of blending in.<BR /><BR />2. When resistFingerprinting is enabled, navigator.hardwareConcurrency&nbsp;<BR />is spoofed to a fixed value of 2, based on a 2017 Mozilla statistic&nbsp;<BR />showing most users had 2-core devices at the time. In my testing, this&nbsp;<BR />value now adds around 4.5 bits of identifying information, since most&nbsp;<BR />devices today report 4+ cores by default. An updated statistic reflecting&nbsp;<BR />current hardware trends might result in a more common, less distinctive&nbsp;<BR />value.<BR /><BR />Both findings came from comparing a hardened Firefox profile (custom&nbsp;<BR />user.js) against Mullvad Browser on Cover Your Tracks, then investigating&nbsp;<BR />the source of each remaining difference.<BR /><BR />Thanks for your work on privacy in Firefox <span class="lia-unicode-emoji" title=":red_heart:">❤️</span></P> Mon, 21 Sep 2026 12:48:01 GMT A7 2026-09-21T12:48:01Z https://connect.mozilla.org/t5/discussions/resistfingerprinting-inadvertently-increases-uniqueness-dnt-auto/m-p/138870#M56435 <P>Hello Mozilla,<BR /><BR />I'd like to share two findings about Firefox's fingerprinting resistance&nbsp;<BR />(resistFingerprinting) that I believe are working against their own goal&nbsp;<BR />of making users less unique, rather than more.<BR /><BR />1. Enhanced Tracking Protection automatically enables the Do Not Track&nbsp;<BR />header, and this cannot be disabled without also disabling tracking&nbsp;<BR />protection itself. According to my testing on EFF's "Cover Your Tracks"&nbsp;<BR />tool, sending DNT actually adds around 1.9 bits of identifying&nbsp;<BR />information, because relatively few browsers send it today, making it&nbsp;<BR />counterproductive to the goal of blending in.<BR /><BR />2. When resistFingerprinting is enabled, navigator.hardwareConcurrency&nbsp;<BR />is spoofed to a fixed value of 2, based on a 2017 Mozilla statistic&nbsp;<BR />showing most users had 2-core devices at the time. In my testing, this&nbsp;<BR />value now adds around 4.5 bits of identifying information, since most&nbsp;<BR />devices today report 4+ cores by default. An updated statistic reflecting&nbsp;<BR />current hardware trends might result in a more common, less distinctive&nbsp;<BR />value.<BR /><BR />Both findings came from comparing a hardened Firefox profile (custom&nbsp;<BR />user.js) against Mullvad Browser on Cover Your Tracks, then investigating&nbsp;<BR />the source of each remaining difference.<BR /><BR />Thanks for your work on privacy in Firefox <span class="lia-unicode-emoji" title=":red_heart:">❤️</span></P> Mon, 21 Sep 2026 12:48:01 GMT https://connect.mozilla.org/t5/discussions/resistfingerprinting-inadvertently-increases-uniqueness-dnt-auto/m-p/138870#M56435 A7 2026-09-21T12:48:01Z