Per http://caniuse.com/css-gradients. IE9 does not support linear gradients. IE10 and IE11 implement the standard syntax. There was never an "-ms-linear-gradient" in any stable release of IE.
Previously removed from:
- (2013) jQuery ULS: https://github.com/wikimedia/jquery.uls/pull/114
- (2013) MobileFrontend: https://gerrit.wikimedia.org/r/#/c/72223/
- (2015) OOjs UI: https://gerrit.wikimedia.org/r/#/c/213523/
Remaining usage: (search)
- MultimediaViewer: mmv.mixins.less
- Vector: jquery.ui.button.css