Why should i use Vivaldi when i also can use Firefox and Classic Theme restorer? Let's see... Vivaldi is Open Source Chromium with a bundled closed source app

Why should i use Vivaldi when i also can use Firefox and Classic Theme restorer? Let's see... Vivaldi is Open Source Chromium with a bundled closed source app (Want to see that is true? Open Vivaldi task manager, kill the webview Vivaldi process, and UI disappears, but browser keeps running) to create the UI which is thanks to how it is created highly exploitable. No thanks, go away!