Improved startup speed
I was reading one site that reported Vivaldi was slower than other browsers. I haven't noticed much slowness, per se, but I have noticed a considerate difference in startup time compared to Firefox and Chromium on multiple machines and multiple OSs. From my Raspberry Pi to my laptop (a high end one but purchased three years ago or so, which runs Ubuntu 18.10 and Windows 10 with the April 2019 update preview), startup is just considerably slower. I think it may have to do with the custom UI. I know it's not really a feature request, but improving the startup speed would help. Take note that both Vivaldi and Chromium are set to not keep running in the background when closed. I'm talking cold startup. Please improve the startup speed in a future release.
@MikeRL100 It would be interesting to know how much time you are actually speaking of. "Slow" does not mean a lot in the absence of some frame of reference.
The software on this machine takes between half a second and 23 seconds to open, with all browsers opening in the 1-4 second range, Vivaldi among them opening in about 3 seconds.
What is "slow" on your system?