The only way I can get this to happen without an ad blocker is to zoom the content above 100% (which, admittedly, is an issue as that shouldn't be happening). At 100% or below though, I can't reproduce this on Firefox using Windows or Mac. Obviously, your ad-blocker is not at fault here since I can see ads in your screenshot so double-check your zoom (I know you likely have since you mentioned 80% but it's working fine on my end up to 100% so it's worth checking again). At some point, we'll be redoing the layout in a more modern way that should likely fix issues like this but for now, this workaround is going to be needed for those seeing this behavior without an ad blocker.
I'm experimenting now to see if there's some way to stop it in the meantime but in my very quick tests, it's not looking like it as it appears to have something to do with how Firefox zooms specifically (I don't see the same behavior in Chrome or Safari).
Edit: I just had a thought - is your OS scaling set to something other than 100%? I ask because things do look a little big in your screenshot and I'm wondering if that's what's causing the weird behavior at 100% in Firefox as it seems to react poorly to zooming for whatever reason.
I'm experimenting now to see if there's some way to stop it in the meantime but in my very quick tests, it's not looking like it as it appears to have something to do with how Firefox zooms specifically (I don't see the same behavior in Chrome or Safari).
Edit: I just had a thought - is your OS scaling set to something other than 100%? I ask because things do look a little big in your screenshot and I'm wondering if that's what's causing the weird behavior at 100% in Firefox as it seems to react poorly to zooming for whatever reason.