MozOsxFontSmoothing returns "" on mac, while on windows (and probably other platforms too) it returns undefined
getComputedStyle(someElement).MozOsxFontSmoothing in resistfingerprinting mode returns "" on mac, while on windows (and probably other platforms too) it returns undefined. I don't know how big of a deal this is since the user agent already exposes the platform, but this could be potentially used to fingerprint a user.