The addon is responsible for, that the CPU usage with the new version is too high on Firefox! I searched for the cause for a long time, I turned off the kaspesky addon and the problem was gone. Please fix it quickly!

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.

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