A simple extension for Chromium that fixes YouTube thumbnails in Russia
YouTube's cdn yt3.ggpht.com seems to be blocked in Russia, so the thumbnails that rely on this specific cdn won't load. This extension redirects all yt3.ggpht.com requests to yt4.ggpht.com.
If yt4.ggpht.com suddenly gets blocked too, you can always change redirect host option in the rules.json file to yt5.ggpht.com and so on.
Same solution. Now extension also redirects all lh3.googleusercontent.com requests to yt4.ggpht.com.