Got here from @buyfromeu after switching browsers (from firefox to vivaldi) and making Qwant my search engine of choice.
Honestly I love @Vivaldi and I wish I knew of it beforehand. It has all sorts of nice features including this mastadon integration.
I’m sorry to break it to you, but Vivaldi is built on the Chromium engine, which is the same engine used by Google Chrome. As a project it depends on Google which is not an EU company.
If you have to chose a fork from either Google or Mozilla, I’d say Mozilla is the least evil. I would suggest Mullvad browser as a better EU substitute. With either librewolf or Icecat as runners up (although not sure if EU based)
There is also ladybird which is a entirely new engine and not based on either Google or Mozilla’s work. It is open source and non profit but I’m not sure if they are based in the EU.
Enjoy Mastodon!