On a page such as https://www.mediawiki.org/wiki/Talk:Watchlist_wishlist/Archive_1 , I see in the console of Firefox 42.0:
Exception in module-execute in module mediawiki.storage: load.php:178:216 SecurityError: The operation is insecure. DOMException [SecurityError: "The operation is insecure." code: 18 nsresult: 0x80530012 location: https://www.mediawiki.org/w/load.php?debug=false&lang=it&modules=ext.centralauth.ForeignApi%7Cext.echo.api%2Cinit%7Cext.eventLogging%2CnavigationTiming%2Cthanks%2CwikimediaEvents%7Cext.eventLogging.subscriber%7Cext.gadget.Edittop%2CHotCat%7Cext.thanks.flowthank%7Cext.thanks.jquery.findWithParent%7Cext.uls.eventlogger%2Cpt%7Cext.visualEditor.targetLoader%7Cext.wikimediaEvents.loggedin%7Cjquery.checkboxShiftClick%2CgetAttrs%2ChighlightText%2CmakeCollapsible%2Cmw-jump%2Cplaceholder%2Csuggestions%7Cmediawiki.ForeignApi%2CsearchSuggest%2Cstorage%7Cmediawiki.ForeignApi.core%7Cmediawiki.api.watch%7Cmediawiki.page.ready%7Cmediawiki.page.watch.ajax%7Cschema.GeoFeatures%2CNavigationTiming%2CSaveTiming%2CUniversalLanguageSelector%7Csite&skin=monobook&version=1a57b17b27a3:73] load.php:178:254
The line in question is:
,data){var msg,e=data.exception,source=data.source,module=data.module,console=window.console;if(console&&console.log){msg=(e?'Exception':'Error')+' in '+source;if(module){msg+=' in module '+module;}msg+=(e?':':'.');console.log(msg);if(e&&console.error){console.error(String(e),e);}}}mw.trackSubscribe('resourceloader.exception',log);mw.trackSubscribe('resourceloader.assert',log);$(function(){var loading=$.grep(mw.loader.getModuleNames(),function(module){return mw.loader.getState(module)==='loading';});loading=$.map(loading,function(module){return mw.loader.using(module).then(null,function(){return $.Deferred().resolve();});});$.when.apply($,loading).then(function(){mwPerformance.mark('mwLoadEnd');mw.hook('resourceloader.loadEnd').fire();});});window.mw=window.mediaWiki=mw;}(jQuery));(function(mw,$){var tasks=[],maxIdleDuration=50,timeout=null;function schedule(trigger){clearTimeout(timeout);timeout=setTimeout(trigger,700);}function triggerIdle(){var elapsed,start=mw.now();while(tasks.Details provided for the error:
dom.storage.enabled is true as by default and dom.storage.default_quota is set to 10240, doing "clear website offline data" from the history menu doesn't change anything so I think the localStorage space can't be at fault; disabling NoScript's blocking and AdBlockPlus for the page doesn't change anything.