Number of logical processors is detectable from web content
The number of logical processors is detectable from web content. Currently, this can be done using https://github.com/oftn/core-estimator:
The total number of cores available to the user agent can already be approximated with high accuracy given enough time using the polyfill in the appendix on a system with low to moderate system load.
But soon this is getting exposed directly: https://bugzilla.mozilla.org/show_bug.cgi?id=1008453