I’ve been having issues with this as well, to the point that I simply could not visit the website on my phone… I have managed to do it though, here’s what I did:
1) If you’re using Chrome on your mobile, then go into settings, then Content settings and make sure ‘block pop-ups from all sites’ is checked. But, you also then need to go into ‘website settings’ (it’s in the same section), then scroll through to find the STW URL, click on this and then make sure that pop-ups aren’t allowed in there (they were on my phone, despite being disallowed in the global settings)
2) I also installed 360 Security on my phone, which has its own pop-up blocker amongst other things, it looks to be a useful app to have on your phone anyway.
So, those steps have worked for me, no more pop-ups and trouble free browsing of the site, huzzah. Hopefully this helps someone else in their frustration!