Few days ago I noticed that my Firefox alt-left, alt-right keyboard shortcuts are not working anymore.. As I am using the keyboard extensively especially those 2 hotkeys and I was very annoyed by this problem. I was sure that this trouble was generated by one of my many extensions. Due to the large number of extensions installed disbaling them one by one was not a practical sollution. So I checked all with KeyConfig and found a bug in DuplicateTab extension. I like this extension because it can clone the browser history to the new tab along with the url so I checked the extesion and searched for an update but Firefox said one was not available.. I then went to extension's page and found out that there is an update indeed.. Installed it and everythings got back to normal.. Pretty weird that Firefox's extension manager didnt noticed me about the update.