What exact combination of circumstances is required to trigger the multi second wait time?
Load: 4.34s, 5.14, 2.96, 3.35
DOMContentLoaded: 3.65s, 4.56, 2.92, 3.33
Finish: 13.14s, 10.77, 8.49, 12.02
So it's getting a bit faster over time, but still heinous, and crucially, it isn't hanging on requests. Individual asset GET/POST requests are taking tens of ms, worst was a few parallel 254ms GETs on a cold start. Usually 50-70ms. But there is a flurry of requests, then a period of very few requests until 5s after init, then another flurry.
Firefox 119.0 Ubuntu 22.04 uBlock Origin, Privacy Badger
Same OS, chrome 115.0.5790.170, no blockers, youtube is much snappier, it still definitely takes a few seconds to paint thumbnails, but it's basically done by 5s. DOMContentloaded is never more than 1.75s, finish <8s.
Firefox private window with blockers off has similar time statistics. But actually doubleclick.net is still getting bounced.