Prompt before closing
This may already be a feature and I just can't find it: Prompt Before Closing. I have never wanted this in any other browser, but it would be seriously useful in Vivaldi. I really like the Web Panel feature and, once I am logged in to all useful accounts in Web Panels, I love being able to take a quick, half-page, glance at different sites. Only problem is, if I accidentally close out of Vivaldi, I have to log in to everything again. I'd like a prompt that says, "Are you sure you want to close Vivaldi."
I'm surprised to find this a year old with no responses. Is there not a way to turn this on? I hated when firefox removed the close prompt, but you could turn it back on by setting browser.tabs.warnOnClose.
There are times when I accidentally hit Win+Shift+D instead of ^W (Win+Shift+D is mapped to close window on my Linux box). I realise you can start the browser back up and hit ^Z (if you don't accidentally open a tab or do something that erases the undo stack), but I'd rather just get a prompt to prevent me from closing multiple tabs.
If not, I might take a stab at writing an extension if there's an API for trapping browser on-close events.