Use of prefixes in tests

I notice that webperftestharnessextension.js [1] has a lot of 
browser-specific prefixes and that [2] fails in gecko because 
"TypeError: this.performanceContext.webkitMark is undefined".

Please don't add browser-specific features, including prefixes, to the 
shared test repository, even if you make some attempt to be "fair" and 
have one non-standard codepath per well-known implementation.

Can I request that the owner of these tests fixes them? If this isn't 
possible I will make the necessary changes myself.

[1] 
https://github.com/w3c/web-platform-tests/blob/master/user-timing/resources/webperftestharnessextension.js
[2] 
https://github.com/w3c/web-platform-tests/blob/master/user-timing/resources/webperftestharnessextension.js