We mentioned a way to do this in the article, One Firefox Toolbar to Rule Them All, here at Lifehack, but this extension makes things a little simpler when it comes to just altering the menu bar.
The Personal Menu Firefox extension works in a similar manner to Tiny Menu, which puts all the menus [File, Edit Bookmarks etc] under one parent menu. However, Personal Menu has a few small differences.
The first is you can select which menus you want available on the toolbar. Each menu drop down is changed to a button.
Personal Menu’s real strength is in the custom button you are able to create that will only feature a list of options in the menu that you personally want in there. This is ideal if there are only a few items you frequently use from the menu bar and want quick access to.