It doesn't skip ads, but mutes the sound, but the actual track doesn't play. The playlist simply stops at the ad.

works flawless, idk what everyone else is complaining about
still fully works in the latest spotify build
this extension is straight-up goated, just try it
don't listen to others, trust me, just give it a try

doesnt work anymore, spotify detects it and shows a banner about refreshing the page

Use uBlock Origin instead:
https://addons.mozilla.org/en-US/firefox/addon/ublock-origin/

Blocks ads on spotify but it takes a few seconds

un asco total es una broma de mal gusto

works