In MW 1.31.10 LTS I get this console error
Exception in module-execute in module ext.favorites: load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=monobook&version=1e4vcjv:177 TypeError: Cannot set property 'favorite' of undefined at load.php?debug=false&lang=en&modules=ext.favorites|site&skin=monobook&version=1f4gm5l:2 at mw.loader.implement.addedfavoritetext (load.php?debug=false&lang=en&modules=ext.favorites|site&skin=monobook&version=1f4gm5l:3) at runScript (load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=monobook&version=1e4vcjv:162) at checkCssHandles (load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=monobook&version=1e4vcjv:162) at execute (load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=monobook&version=1e4vcjv:163) at handlePending (load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=monobook&version=1e4vcjv:159) at markModuleReady (load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=monobook&version=1e4vcjv:161) at runScript (load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=monobook&version=1e4vcjv:162) at checkCssHandles (load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=monobook&version=1e4vcjv:162) at execute (load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=monobook&version=1e4vcjv:163)