I know that many reject Vivaldi, because he is not entirely FOSS and only listed as Free-Proprietary, although I think that it is not at all fair to compare it for this with others in this category. The small part, about 5% of the code is obfuscated for good reasons. However, it does not prevent the user from modifying it to their liking and it is even encouraged by Vivaldi, but it does prevent large companies (Google) from making a fork of Vivaldi and thereby destroying this still small cooperative.