Extension:DismissableSiteNotice

The DismissableSiteNotice extension allows users to close the manual>Manual:Interface/Sitenotice|sitenotice, using cookies.

Configuration
This extension provides two configuration parameters:

Integer. The value is stored inside a cookie. When a user decides to close the sitenotice, the current value of $wgMajorSiteNoticeID is saved as well and the closed notice is not shown again. $wgMajorSiteNoticeID now can be incremented when a new text is set up as sitenotice. If $wgMajorSiteNoticeID has inbetween been incremented, then the sitenotice is shown again, even if the user closed an older sitenotice before.

This allows to set whether or not it should be possible for anonymous visitors of the wiki to dismiss the sitenotice shown. Defaults to "false". Available for MW 1.25 +

Usage
When you add a new sitenotice and want everyone to see it, change the number on the created page "MediaWiki:Sitenotice id" by one (e.g. if it would be 5, you'd replace the page with the number 6 and so on).

The extension behavior is that it will remember the dismissal by the user and only reset after the number in  has been raised. This allows a wiki to make minor updates to a notice without causing it to show again for everybody.