Most open source browsers are a reskin of actual open source browser development. E.g. Brave and Vivaldi are skins on top of the actual Chromium project, librewolf and others on Firefox's components, and Orion and others on Safari's components. Only a rare few browsers e.g. Dillo or Ladybird are actually independent and it shows in that those browsers are nearly unusably slow, compatibility limited, and insecure (that's not a diss on them, they are still awesome projects for their own reasons).