Yesterday Kaspersky announced on its user forums that a fix has been developed for the excessive CPU usage we're experiencing with version 2.4.33.0, and a new version will be available soon. (The current, buggy version was released 25 days ago, and I wish a fix had been released more quickly.) In the meantime, downgrading to version 2.3.16.0 corrects the problem. Click "See all versions" under "More information" in the left column of the Kaspersky Protection 2021 add-on page. Then download and allow the installation of version 2.3.16.0. After installation, disable Automatic Updates in the extension's properties.

I've been having problems with heavy resource use on firefox, particularly of CPU. After checking individual exenstions I found that Kaspersky browser extension was the culprit and seriously hogs both RAM and CPU. Turning it off solves the resource problem.
As I have full (paid for!!!!) Kaspersky suite installed I'm not sure what the logic is of having to instal another app to manage browsing for the same product.
I think the developers need to look at this issue.

Ottima protezione, e avvisi utili per la prudenza

Kaspersky Firefox Addon version 2.4.33.0 is using 40% of CPU. Revert to verstion 2.3.16.0 solve problem.

Satisfactoria, me siento seguro