@ legacy twitter: Please re-read my post. I didn't say twitter wasn't working with extreme mode. I said legacy twitter not working anymore with extreme mode since a few months back.
But: Since June 4th I have it working again. I did some testing and finally added ma.twimg.com on the black list in adaway. It didn't make any difference. I didn't reboot the device and didn't restart consciously opera. But 1-2 days later finally twitter loaded in legacy/classic design mode again instead of the "normal"/desktop design which requires cookies to be enabled to show content.
So, if Opera didn't do any changes to their "proxy"-server settings I guess blocking that url/domain that hosts twitter's js files using adaway seems to work even though initially it didn't look like.
@ search engines: Thanks for the hint! Of course my favourite one uses post, too... 🙂 But at least I now can add some more.