As soon as the addon was updated to 2.9.9, the browser behaved like a crawl. Slow. Sluggish. Choppy. One core full load, so 25% CPU usage all the time.
As soon as I downgraded back to 2.9.8 - issue gone immediately.
And I use this source, because Pale Moon does not support WebExtensions: https://addons.palemoon.org/releases/i-dont-care-about-cookies/
See also here: https://forum.palemoon.org/viewtopic.php?f=44&t=21818
