Get ScriptInstaller, then navigate to User:Zvn/confirmwatchlistrollback.js and click "Install" at the top.
(This can be used on any-language Wikipedia.)
{{
subst:lusc|1=User:Zvn/confirmwatchlistrollback.js}}
on the bottom of
your common.js page or
your skin.js page.(This can only be used on the English Wikipedia.)
{{
subst:iusc|1=User:Zvn/confirmwatchlistrollback.js}}
on the bottom of
your common.js page or
your skin.js page.