Not a bug, but this seemed like the best place to post my question.
On mobile, when I go to worldofwarcraft.com, tap on the hamburger menu and select Forums, it opens up a completely separate app.
What app is this? It seems mostly like Chrome, but not quite.
I’m pretty sure it’s whatever app your device has configured to open that kind of link. It’s not a website setting, it’s a “your device” setting.
For instance, on my mobile device, that sequence just opens the link in the same browser. Ditto with my desktops. If any of my systems tried opening a link using a different browser, or a new window in the same browser, I would hunt down the misconfiguration in my system and set it right.