When I first accessed
https://pt.wikibooks.org/w/index.php?title=Alfabeto_dos_animais/T114278&action=edit&redlink=1
I got this on Firefox 42.0:
{ "errorMessage": "TypeError: $ulsTrigger.tipsy is not a function", "url": "https://pt.wikibooks.org/w/load.php?debug=false&lang=pt&modules=ext.centralNotice.bannerController%2CchoiceData%2Cdisplay%2CgeoIP%2CkvStoreMaintenance%2ClegacySupport%2CstartUp%7Cext.centralauth.centralautologin.clearcookie%7Cext.gadget.MwUi%7Cext.uls.init%2Cinterface%2Cpreferences%2Cwebfonts%7Cext.visualEditor.desktopArticleTarget.init%7Cext.visualEditor.track%2Cve%7Cjquery.byteLength%2CbyteLimit%2Ccookie%2CtabIndex%2CtextSelection%2Cthrottle-debounce%7Cmediawiki.Title%2CUri%2Capi%2Ccldr%2Ccookie%2CjqueryMsg%2Clanguage%2Ctemplate%2Ctoolbar%2Cui%2Cuser%7Cmediawiki.action.edit%7Cmediawiki.action.edit.styles%7Cmediawiki.language.data%2Cinit%7Cmediawiki.libs.pluralruleparser%7Cmediawiki.page.startup%7Cmediawiki.template.regexp%7Cmmv.head%7Cskins.vector.js%7Cuser.defaults&skin=vector&version=b2678012c992", "lineNumber": 33, "columnNumber": 323, "errorObject": {} }
The error didn't happen after a page reload, neither on debug mode.
Looks like this is the only script using it:
https://github.com/wikimedia/mediawiki-extensions-UniversalLanguageSelector/blob/b01c7d69b129b9fb48e28b833c914017ecd5dbb2/resources/js/ext.uls.interface.js#L225-L299
Please check the dependencies on the modules you are using.