Bug 1679800 - Enable browser_readerMode.js. r=peterv

Differential Revision: https://phabricator.services.mozilla.com/D98433

toolkit/components/reader/test/browser.ini

@@ -5,7 +5,6 @@ support-files =
   readerModeNonArticle.html
   readerModeArticle.html
   readerModeArticleHiddenNodes.html
-skip-if = fission
 [browser_readerMode_cached.js]
 support-files =
   readerModeRandom.sjs