Analyzing it, you seem to send/receive thousands of DOM requests / Events, to be true, you seem to endlessly check getLoginStatus in your SSO for some reason even if there is no user interaction, hitting the cache of the browser engine constantly (getCookie in this case Gecko/Firefox, but it happens in Chrome too):
With a few tabs of your website open (3-4) this adds up to completely freezing the browser and clocking up the CPU to full potential (even on Ryzen 7 3700X at the moment). I don't know why you're checking the login status 3000 times in 5 seconds, but it sounds quite odd to me.
Every tab uses pretty much exactly 1 CPU core, with multiple tabs open, the browser starts to strugge answering the requests in the base process (like getCookie, which are not in the WebContent engine threads, neither is the GC):
Hey, I see you actually do use Dynatrace and it didn't catch it? Happy to help out to help your customer experience (not completely selfless though ;-)). Just kidding, but would be nice if somebody could look into that, it's really highly annoying and makes using the site/community less fun.
I'm not a SaaS user (Managed installation), so that may be connected ("SaaS login" always shows for me, even if i'm logged into my account - and can obviouisly post).