Couldn't reproduce the issue. Do you use custom filters? It can also happen if you enable almost every filter possible.The latest Adguard Browser Extension for Firefox (FF ESR x64) takes mostly 100% CPU loading.
Every new tab takes nearly 30 seconds 100% CPU loading.
A click at the adguard extension show the message "extension is loading" and CPU goes 100% until the Extension shows up.
It's not a problem of the browser extension. After deinstalling the extension the problem was away for short time only. I dont know what this problem is but it's not from the adguard extension, sorry.Couldn't reproduce the issue. Do you use custom filters? It can also happen if you enable almost every filter possible.