This is a piece of code downloaded from Mozilla servers to re-enable extensions, which are other pieces of code you download from Mozilla servers. If your threa

This is a piece of code downloaded from Mozilla servers to re-enable extensions, which are other pieces of code you download from Mozilla servers. If your threat model includes not trusting Mozilla servers then you've presumably disabled browser extensions (or sideloaded them) and this issue is irrelevant to you. If you do use extensions and get updated versions from Mozilla I don't see any way in which this increases your attack surface.