hit firefox button and then hit the add-on button. when screen comes up go down to the bottom right corner and choose browse all add-ons. once there, in the search box in the upper right corner type yahoo mail button. it should list all your options. find one you like and install. you might have to repeat all steps for each email button(gmail,hotmail,etc.)but they might have an add-on that gets them all, just look through them.