I am sorry since I'm not fluent in Your native language,so I am using a common language to answer this ,hope you are good with it (en-US) . Well the crash shows this happens due to iCloud extension . A bug was filed way back on ff 35 on this and it seems it still present : https://bugzilla.mozilla.org/show_bug.cgi?id=1097138 First shot: Disable it and open firefox in safe mode [https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Safe Mode] and see whether it works or not. Edit 1: Desactivarlo y abrir Firefox en modo seguro [https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Safe Mode] y ver si funciona o no . Another shot : Uninstall it from Menu > addons > Extension ,and then open firefox . Edit 2: [Desinstalarlo de Menú> complementos > Extensión y abra Firefox ] One of question already mentioned this : https://support.mozilla.org/en-US/questions/1063944 PS: I have tried to translate en-US into your native language using google translator which i am not much sure about accuracy ,so please don't mind .