Electronic Frontier Foundation (EFF), to examine browser fingerprinting. The research proved that 94.2% of all the fingerprints of internet browsers, excluding Tor browser’s fingerprints, are unique.
Accordingly, the server can associate the access to analyze the browser for tracking. Such association can lead to de-anonymization of users.
Fingerprinting is a serious threat to Tor’s.
Tor Browser Fingerprinting:
HTTP Header:
in HTTP header, the User-Agent’s value is constant. The version of a user’s Tor browser can be obtained, Accept-Language within the HTTP header is “en-us,en; q = 0.5”, while in version 5.0, or following versions, it is “en-US,en;q = 0.5”.
Size of the Content Window:
The window screen property can be utilized to identify Tor browser’s content window size. (CSS) media queries can easily deanon you!
Fonts:
a. JavaScript with CSS.
b. Utilizing 
CSS is evil!!!
SSE2 Test:
Stream SIMD Extensions 2 (SSE2) can be used to detect if the user’s CPU
Refresh Rate:
A drawing’s refresh rate in a display can deanon you too