961
YouTube's ad problem just got worse: Users now seeing 90-second unskippable ads!
(www.androidauthority.com)
This is a most excellent place for technology news and articles.
On PC it's a browser extension that works best with Firefox (uBlock Origin is generally recommended). It also works on Firefox for Android. You will likely need separate extensions for each browser and device you use. I don't think Firefox syncs extensions between phone and desktop.