On Windows, if the user installs Chrome, it's installed into the user's home directory (local application data or something). This means the user does not need admin rights to either install or upgrade Chrome.

There are several ways to update programs on Windows without needing admin rights:

- You could do it as Chrome does and have a per-user install. I don't think Mozilla wants to do this.

- You could install a service or a scheduled task to do the work for you.

- MSI updates can be installed without admin rights if they're Authenticode signed, and Mozilla does have a valid Authenticode digital certificate.