Browsers cut off the page at left-side.

Yes, I've found that this site is viewed correctly with a larger monitor only. I have an older and smaller amd that's the problem. Also phone doesn't work. Yes a horizontal scrollbar would be nice.

If I shrink my firefox window, I see the issue now too. If what you want are scroll bars, it looks like this is the bit of CSS that makes them disappear. It's from common.css. The "overflow-x: hidden" hides the X (horizontal) scrollbar. If you go into the firefox console, you can edit it or toggle it off and get scroll bars back.

body {
font:12px 'Noto Sans','Lucida Grande','Lucida Sans Unicode',Geneva,Verdana,Sans-Serif;
color:#707070;
background:#eee;
background-image:linear-gradient(to bottom,#d7d7d7 0%,#eeeeee 116px);
overflow-x:hidden;
cursor:default;
}

If you always want that enabled instead of having to manually toggle it on, perhaps you could override it using a local trick like this one:
ffeathers.wordpress.com/2013/03/10/how-to-override-css-stylesheets-in-firefox/

This happens to me too. I use Safari.

Maybe if a developer picks up on this thread, they could consider adding an option under the preferences or theme selection to toggle the X & Y bars on/off. Maybe here?:

http://en.lichess.org/account/preferences/game-display

or maybe a new set of preferences for site-display since this doesn't only apply to games?

Don't know about X Y bars but a simple option would be a horizontal scrollbar.

The X bar is the horizontal scroll bar. I just tried this Firefox Add-on that makes overriding style sheets easier, and you can use it to enable the horizontal (X) scroll bar.

addons.mozilla.org/en-US/firefox/addon/stylish/

Once it's installed you can click "Write new style", give your style a name (e.g. Enable Horizontal Scroll) and then paste this into the script area and then save it:

body {overflow-x: visible !important;}

Then you can use the add-on to toggle the scroll bar on and off.