The browser the changelog links are built with, the same ones the Git SCM offers. Each one asks for the URL of the repository on its web frontend, without the commit part that Jenkins adds itself.

(Auto) guesses it from the remote: a github.com, gitlab.com or bitbucket.org remote gets its own frontend, a remote shaped like a Gerrit (its host name, an /a/ clone path, a plugins/gitiles path, or the SSH port 29418) is linked with the gitiles URLs, and anything else with the GitHub ones.

A browser set here wins over Browser URL, which in turn wins over the guess. Use Browser URL for the two Gerrit forms, and a browser here for the frontends whose links cannot be derived from a URL alone.