Manual:$wgUniversalEditButton

Edit user interface: $wgUniversalEditButton
Enable the UniversalEditButton for browsers that support it.
Introduced in version:1.14.0 (r41916)
Removed in version:still in use
Allowed values:(boolean)
Default value:true

DetailsEdit

Enable the UniversalEditButton for browsers that support it (currently only Firefox, Opera and Chrome with an extension).

See http://universaleditbutton.org for more background information.