[Twirrim]

You don't even have to do that.

On reddit, go to your preferences. Down under beta test you'll find "Use the redesign as my default experience"

Disable it.

[pubby]

The problem is that reddit randomly ignores this and switches back to the redesign on a whim.

[Twirrim]

Interesting. It has never failed for me since turning it on soon after the redesign landed.