Out of memory crash
Vivaldi memory management needs to get better. Using my laptop on Win7 X86 with its staggering 3Gb of memory while away from home on business, and with Vivaldi, an email client, and TeamViewer open, I repeatedly get the warning that my machine is low on memory. If I ignore the warning too long and don't close something, the Vivaldi UI crashes, leaving a slew of zombie processes. I don't have this problem on the desktop at home with its 10Gb of RAM, but should not have it here, either. There's no reason why Vivaldi should have to gobble up all available memory.
vivaldi's taking a leak (leaking memory). i think that used to be the bane of firefox as well.