DeviantAnyWhere and dA Message Notifier is a pretty cool extension for Chrome but there are some of us that are using Opera and I can imagine that there's a demand or a request for these chrome extensions to come down to Opera, that is pretty slim to none since there's a majority that are running chrome only and something like that request would be fallen to deaf ears.
However, there is a way and it's easy to do.
This only works with versions 15 or over, so for those who have an older version, you might need to update it.
Anyway, all you need to do is download "Download Chrome Extension"
Link to get the extension
Then head over to the google chrome version of said extensions ( DeviantAnyWhere & dA Message Notifier ) and download it, it may give out a pop up about an unknown extension that requires you to go to the extension menu, click go and click on install twice and BAM!
You've got DeviantAnyWhere/dA Message Notifier on Opera.
But this tutorial isn't for these extenstion exclusively, it can pretty much work on any Chrome Extension, unfortunately this wouldn't help for Chrome Apps, it's a whole different breed.