Issues with keyboard shortcuts
We know about a bug with Backspace on some Linux systems.
PS: Please, you are using a very, very old version of Vivaldi.
Current Latest Snapshot version is found at https://vivaldi.net/en-US/ or can be loaded by package update from Linux repo.
I am now running latest snapshot, but I had to download it manually. I can't find any information regarding a Ubuntu repository for Vivaldi. Is there something like that?
I will try running latest snapshot now and see if my problems go away.
After you installed the Latest Snapshot the repository will be added for future use.