Help:Extension:GlobalPreferences

The GlobalPreferences extension allows user preferences to be set for all wikis in a wiki farm. This means that users can change their preferences for all linked wikis without having to visit each in turn. Local exceptions can be set for individual wikis.

Extra preferences page
The extension adds a second preferences page, accessed from the  tab of Special:Preferences. This GlobalPreferences page mirrors the normal preferences page (with some items removed because they are not applicable globally) and for each preference it adds a new checkbox with which the user can select that preference to apply globally.

The GlobalPreferences page is present on all wikis in the family, and changes made via any wiki are mirrored everywhere else. If a wiki has preferences that are only present on some wikis (for example, for an extension that is not installed everywhere) then those preferences must be set globally from one of the wikis that does have those preferences. They'll not appear on other GlobalPreferences page, but they'll not be modified when those other GlobalPreferences pages are used.

Once a preference has been selected to be global, it will no longer be modifiable from the normal preferences page.

Local exceptions
If a preference is set to be global, it will be disabled on the normal preferences page, but a new checkbox will be added under it with which an exception can be made for just the current wiki.