Developer Tools Very Slow
When inspect the DOM in Developer Tools it becomes very slow to expand / collapse the DOM tree nodes or the JSON nodes in the Network / Preview tab. When I say slow I mean it's taking up to 30 seconds just to expand one node. I'm using the latest Vivaldi on Ubuntu 15.10. Initially Developer tools is responsive but usually within 10 minutes from starting Vivaldi with Developer Tools open it gets to the point of not being usable. The browser itself is responsive though - just the Developer Tools is wayyyy tooo slow.
It may not be relevant to what you're seeing but Ubuntu 15.10 is no longer supported: it went EOL on July 28, 2016.
The dev tools seem responsive enough for me on Ubuntu 16.04.
Maybe if you put up your hardware specs, someone might have some comments to offer.
//MODEDIT: Added scheme https: to URL.
Don't forget to also post to what you're working on.
Because I don't suffer anything you described. Tested on Vivaldi forum.
@rowatt Please, don't forget to add a http:// or https:// if you use links here! Otherwise they are relative to forum, not to destination domain.
I can not reproduce slow DOM in Devtools on Ubuntu 16 LTS.
Regarding your problem: Please try to update to a newer Linux Ubuntu 16.x and check if the problem stays or is gone.
@Gwen-Dragon noted re. the http:// and https://.
I'll look out for that in future!