Most important first, then tweaking whenever I feel something more is needed.

i build mine from source 😉

Full tweak the first time (better way to learn every possibilities), then i come back if needed or for an update.

Set and forget. There are lots of Vivaldi features I have t bothered to figure out.

That’s for three reasons. 1) on Linux desktop, everything breaks all the time so I have to re-configure anything 2) I use lots of computers during the day, some of which are shared. That means configuration both isnt possible AND if I get used to it I’ll be useless when I have to do something on someone else’s machine.

I fully customize the browser first, then adjust the settings as needed.
I am now completely migrating all settings with history to new system. The option of transferring all data via synchronization did not work for me.

I tweak it.

I do an initial check, tighten up security settings (especially on Vivaldi...), add some extensions, turn off notifications and autoplay video and audio. Then, if I find I missed something or I notice they aren't acting the way they did before, I'll go back in and tweak again.

I prioritise setting up security and privacy before browsing.

This focuses on:
1. Filter lists and content blocking, especially malicious/phishing domains/malvertising
2. Cookies (no 3rd party, autodelete with whitelists for cookies I want to keep)
3. Disabling browser password manager, form autofill, payment method detection, etc

@Vivaldi, in the beginning I have changed the UI and theme many times, but for several years I am quite happy with the theme and settings it has, which I find comfortable. The only thing that changes is the wallpaper, this is automatically the same of my OS when I change it there sometimes.