I've tested it, it is uBlock. Very fast boot when disabled, several seconds when enabled.

Have you thought about filing a bug report? gorhill (the author) is an active user on HN. I'm sure he would take a look if you provided some logs.

It looks like another addon was phoning home to a blocked resource. I should've tried more combinations first. The best thing I can think of is that it would be cool if uBlock reported when a call from another extension has been blocked.

> it would be cool if uBlock reported when a call from another extension has been blocked

That is the purpose of the built-in logger[1]. By default uBO is not setup to block other extensions' network requests, or those made by the browser itself, one has to configure it explicitly for this to happen[2].

1. https://github.com/gorhill/uBlock/wiki/The-logger

2. https://github.com/gorhill/uBlock/wiki/Behind-the-scene-netw...

Hm OK, must be something else then. Either way, uMatrix blows Ghostery away so this has been fortuitous.

I'm using it now at the recommendation of people here, and you're too right. It's a bit like going from a pogo stick to a McLaren.

That's bizarre! Have you tried disabling everything except uBlock and seeing if that persists? Maybe it's some kind of interaction with other addons causing the problem.

I think that's the next step, I've done things like this before but generally only to troubleshoot outright breakage caused by some addon. Thanks!

My pleasure, I wish you the best of luck with it.

Another user recommended uMatrix as a Ghostery replacement in this thread which I was trying out, and it looks like some Ghostery/uBlock interaction was to blame. My best guess is some Ghostery resource is correctly flagged by uBlock and that the delay I experienced was a request timeout or similar, from Ghostery.

That makes sense, and oddly enough I was just (literally for the first time, 10 minutes ago) looking at switching out Ghostery for uMatrix. Decision made, thanks.