Definitely browser specific for me, too. Palemoon on a old Win 7 machine is fine, Firefox gets the blocking and hung pop-up every time, unless I use a VPN to pretend to be outwith the EU, when Firefox works fine, with no problems.
Seems to me that the apparent location triggers the Trustarc thing initially, so no matter what browser you're using if PPRuNe thinks your outwith the EU then the blocking pop-up won't appear. If you do seem to be within the EU, then it seems that some browsers cannot deal with whatever it is that has changed within the Trustarc GPDR compliance feature. My guess is that Trustarc may have updated something today, and broken some core functionality with some browsers.