There is a choice on the bottom left menu labeled "Old site"; just click on it and voila!
old chess com

@David: In V3 I can't see any chessboard and chesspieces anymore. I am using firefox on linux, hence I might be an exception to the rule, but I find it quite amazing for a web interface.

@David: In V3 I can't see any chessboard and chesspieces anymore. I am using firefox on linux, hence I might be an exception to the rule, but I find it quite amazing for a web interface.
The standard advice is to clear your cookies and your cache - if the problem persists, you would be best off using the Report a Bug feature, which will allow you to capture a screen shot at the same time as logging the issue with the Support team.

@David: thank you for your advice. Unfortunately, it did not work. Where can I report a bug?
As you can see, I do not see any chessboard or piece. Looking at the URL can you see that I was trying to open a game. I am using Linux with Firefox.

Did you try typing www.chess.com/switch (or clicking here)?

@David: thank you for your advice. Unfortunately, it did not work. Where can I report a bug?
Hover over the ? Help icon and the last entry in the pop up menu is "Report a Bug":

Aha, that is why I did not find that feature. If I hover over Help, then the submenu doesn't appear. At least it is in the most logical place, as that was my first action in trying to find that feature.
So I report another bug here: not all submenus appear when hovering.

Hm - best to log a ticket directly then via https://support.chess.com/customer/portal/emails/new. I don't think you can attach a screen shot directly there, but if you've saved the image to Imgur or something like that, you could include a link. You'll get an automated acknowledgement of your request, and then a Support team member will contact you directly about it via e-mail (at which point you could give them the screen shot).

This worries me because I'm thinking of switching to a Linux desktop. I just want to leave windows behind. But if V3 is not compatible, then I'd like to know before I lay down money.

I always switch to V2.... no problems with windows or linux mint 18
Edit: you have to make sure you keep everything up to date.
what is the trick so I can get back to the old chess.com? I cannot play in the new one.