Testing the following extension: https://addons.opera.com/en/extensions/details/bitwarden-free-password-manager/?display=en
With Opera Windows, Chrome Windows, Chrome macOS, and Firefox Windows and the extension's browser action UI behaves as expected. See screenshot: http://imgur.com/ZHDduXv.png
When using the same extension on Opera macOS, the contents of the browser action window are pushed out of bounds and the extension is unusable. See screenshot: http://imgur.com/VLkBlxY.png
I've tried tweaking some of the extension's CSS but it doesn't seem to have any effect. This only happens on Opera macOS.