The issue is with the site; I just replicated the issue on Chromium and Firefox.
I'm marking as "Not a bug" being it's a site error not a bug with Steam itself... but I'm leaving it open so a Valve employee can see it and let the right person know.
I've passed this on to the web team, thanks.
Nothing extracted yet.
I just updated Steam, and now it opens the "Featured Games"-tab when trying to access "Linux"-tab.
The console outputs
"(steam:19019): LIBDBUSMENU-GLIB-WARNING **: Trying to remove a child that doesn't believe we're it's parent."
during launch, I don't know if it's relevant to this issue though.