Quick Command trick
I have problem with Quick Command for a long time. It will hang Vivaldi if I have more that 1000+ bookmarks (not yet count with many tabs). Sometime it will just hang with CPU spike to around 80%, but most of time no movement at all.
Related thread: F2 Quick Commands - takes 40 seconds to find item - 17 tabs
I accidentally find out (just this morning) as long I start with alphabet character, it absolutely will hang my Vivaldi. But... if you start with non alphabet such as numeric Quick Command will work as suppose to be.
!vivaldi or @vivaldi or 1vivaldi or 2vivaldi
Just delete the first character after you finish inputting your search term.
I tested this multiple times, and the result seem consistent.
At least it a good work around for me until it officially handled.
Vivaldi 1.6.689.46 64bit
Vivaldi 1.7.721.3 64bit
Linux/Debian 64bit|32bit sid