Post formatting buttons do nothing

EbonJaeger

On Vivaldi 2.3.1440.60, none of the formatting buttons when writing a post do anything when clicked. There are no errors in the dev console. They do work fine in Edge.

Fake Edit: Same issue on the Flarum forums. Guess I'll post about it there, and leave this here for other people.
Link to Flarum thread: https://discuss.flarum.org/d/19240-post-formatting-buttons-broken-on-vivaldi

JoshStrobl

Vivaldi seems to be having issues with constructing CustomElements at this moment in time, because the same issues also apply to Polymer (instead of Mithris, which is what Flarum uses) which ends up breaking Youtube rendering.

See https://forum.vivaldi.net/topic/34730/failed-to-construct-customelement-the-result-must-not-have-attributes