When clicking on "Merge with" to use the merge tool on Wikidata with Firefox, nothing happens and we get this error in the web console:
Uncaught DOMException: Permission denied to access property "ownerDocument" on cross-origin object load.php:179
With debug=true:
Uncaught DOMException: Permission denied to access property "ownerDocument" on cross-origin object Element.js:301 getDocument Element.js:301 getDimensions Element.js:462 getSize Window.js:216 getSizeProperties Window.js:236 fitLabel ProcessDialog.js:263 emit jQuery setLabel LabelElement.js:171 getSetupProcess Dialog.js:233 proceed Process.js:62 execute Process.js:97 setup Window.js:621 openWindow WindowManager.js:436 Uncaught DOMException: Permission denied to access property "ownerDocument" on cross-origin object Element.js:301 getDocument Element.js:301 getDimensions Element.js:462 getSize Window.js:216 updateWindowSize WindowManager.js:707 updateSize Window.js:454 setup Window.js:622 jQuery 2
It may be linked to T254693.