I want to use performance.now() to measure performance of an extension, but its resolution is limited to 1ms due to cross-origin isolation restrictions. MDN says we need to enable cross-origin isolation to use such features, but how to do this for WebExtensions?
Watchout for over-optimizations 
.
If something takes only few ms to execute, it may not be worth to optimize.
In any case, you can improve precision by re-executing the test case in series (unless there is some caching involved).
EDIT:
Oh, and I just read about similar topic in the new Nightly news: