Browsers historically have had a single HTTP Cache. This meant that if www.a.example and www.b.example both used cdn.example/jquery-1.2.1.js then JQuery would only be downloaded once.
Unfortunately, a shared cache enables a privacy leak.
Browsers are responding by partitioning the cache.
What does this mean for developers? The main thing is that there's no longer any advantage to trying to use the same URLs as other sites. You won't get performance benefits from using a canonical URL over hosting on your own site (unless they're on a CDN and you're not) and you have no reason to use the same version as everyone else (but staying current is still a good idea).
Okay! So shared cache advantages are supposedly getting smaller and smaller due to rightfully implemented security improvements. This reminds me of a related article: Self-Host Your Static Assets by Harry Roberts.