When browsing this site with Opera 31, user agent string
Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/44.0.2403.155 Safari/537.36 OPR/31.0.1889.174
I got the mobile layout, with a burger overflow icon on the top left clearly meant for mobile. I have to use the old Opera, user agent
Opera/9.80 (Windows NT 6.2; Win64; x64) Presto/2.12.388 Version/12.17
To get to desktop layout. Microsoft Edge also shows me the desktop layout
I do not currently own other browsers like Firefox or Chrome, but I have a 3rd party browser on my smartphone that comes with desktop Firefox and Chrome useragent, both of them gives me mobile layout. Based on this info, it seems that the problem lies on this site instead of the browser. Perhaps a useragent detection algorithm misbehaved?