This was my experience...
Hmm, a WebGL application I'm developing isn't receiving my right-click gestures. I guess that's the mouse gesture functionality I remember from Opera. No worries, I'll just change the bindings...
I opened the settings and found the mouse gesture settings easily. Hmm, okay there's this bind to Alt checkbox, I'll enable that.
Back in my WebGL app... Hrm, still not working. On closer inspection I see the Alt binding only works for trackpads. Okay, fair enough... I guess. I'll just change from right-click to middle mouse, or something... Wait, no options for that. Okay, fine I'll just disable the darn thing.
Now my WebGL app works great. Yay!
Hmmm, but I feel like I'm not getting the proper Vivaldi experience without those gestures. I know! Vivaldi is open source, I'll just implement some configuration options myself...
Wait, they only offer tarballs? How the heck do I submit pull requests? Presumably I can't. Alright, I’ll email them asking if they plan to accept pull requests any time in the near future.
Hmm, their contact form keeps failing with cryptic error messages, but never explaining what I did wrong.
Alright, I’ll go to their bug tracker. Okay, I need to sign up. Wait... what? Their bug tracker registration form is also failing but not explaining why.
Okay, to be fair, by this point I'm guessing it's because I'm using an addition (plus) character in my email address. Not supporting that is poor, but not informing me that the email address field is the issue is totally unacceptable.
Alright, I'm far too annoyed at this point. If Vivaldi can't manage an open source project, can't write a working contact form and can't write a working sign-up form then I have very little evidence to suggest they can write a decent browser.
Firefox it is.
it used to barf helpful error messages (including info it should give like internal network details), I reported it and got a thank you email ... and immediately got banned from their forums :)
I'm actually trying Brave now and am quite impressed. It's certainly got some problems (viewing SSL certificate is broken - https://github.com/brave/browser-laptop/issues/2611). However, it's pretty slick and the fact it's a real open source browser is quite promising.
Vivaldi's native tab management far surpasses both Chrome and Firefox. Likewise native mouse gestures work in every place including the speed dial (unlike plugins which attempt to do so on other browsers).
The only thing I miss is tab synchronisation across mobile and desktop devices.
If you're using mobile Chrome on Android, you should seriously take a look at Brave.
But it's source code is available.
Have you or someone looked through them to confirm they contain all of Vivaldi? Do they state this somewhere? Can you compile Vivaldi from them?
I'm not that concerned with not being able to distribute modified versions (freedom 3) since I am unlikely to have the time to contribute quality code unlike Benjamin above ( https://news.ycombinator.com/item?id=13514415#13517798 )
But I do want to be able to compile it myself and tweak & hack it as I like (freedom 1). (We already have freedom 0 and 2).
Of course I would prefer to have freedom 3 too, so that in case I have the time to do more than hacks I could actually contribute.
https://github.com/ograycode/vivaldi-source (not-official mirror)
I'll have to try building it from source.
It's not perfect, but I've found myself having to open up Chrome as a backup less and less often. At this point I think it's been about a month since I've needed Chrome.