The slot name is EXIT_STITIAL_BOXAD_1, sizes passed are 600x400,300x250.
Another note: the modal will be only shown to anonymous user and only on wikis with $wgEnableOutboundScreenExt variable set (Current list of such sites is kept under this URL: http://community.wikia.com/wiki/Special:WhereIsExtension?var=700&searchType=bool&val=0&likeValue=true).
Click here to trigger exitstitial ad
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