Hacky fix implemented.
Hide the sidebar completely if the screen size is not wide enough.
Rationale: If you're looking at the mobile site, you probably just want to check on the vids, your posts, and mentions (all accessible via the menu).
If you really need to see the sidebars, you can force request the desktop site.
Tested and works on my phone (both portrait and landscape, both desktop and mobile requests) - but please test on your various mobile devices