MB 80: Enable Mullvad Browser as a default browser

browser/components/preferences/main.js

browser/components/shell/ShellService.sys.mjs

browser/components/shell/WindowsDefaultBrowser.cpp

browser/components/shell/nsWindowsShellService.cpp

browser/installer/package-manifest.in

other-licenses/nsis/Contrib/ApplicationID/Makefile

other-licenses/nsis/Contrib/CityHash/Makefile

toolkit/mozapps/defaultagent/EventLog.h

toolkit/mozapps/defaultagent/SetDefaultBrowser.cpp

toolkit/mozapps/defaultagent/moz.build

widget/windows/WinTaskbar.cpp

widget/windows/moz.build