It's cool that you use a lot of open source projects. But some of them are under licenses that require the user to be able to download their source code, and it's not obvious right now where (for instance) your Webkit code is. You should probably fix that.

According to that, it seems that Vivaldi uses a lot of GPL'd and LGPL'd libraries, and it's not clear that Vivaldi is in compliance with the copyleft requirements of those licenses, nor is it apparent which license Vivaldi is released under as well (be it a FOSS license, some EULA, etc.).

There are also a lot of libraries listed that are licensed under the Mozilla Public License, which is incompatible with the GNU GPL. Distributing this therefore might not actually be legal, regardless of whether or not it's released under a FOSS license, since those two license families have conflicting requirements for derived works (including works which use those libraries).

YMMV, IANAL, etc., but this thing's running the risk of legal technicalities killing it in the crib.

Please just give us a native window that works like the rest of the application windows on my OS though. What's the need for customizing the UI so that it doesn't fit in with the OS?