Hmm, interesting question. Firefox has some support for Right-to-Left languages where things are justified to the right side of the screen, but I don't know whether that applies to the menu bar, and anyway, if you ONLY want to change the menu bar, a global change probably would be aggravating. Most likely you will need to delve into the community supported (i.e., not officially supported) world of modifying your Firefox user interface through style rules in a userChrome.css file. A good site to ask about that is this subreddit: https://www.reddit.com/r/FirefoxCSS/ I also have a general website with more information, but I don't have anything about moving the menu bar to the right: https://www.userchrome.org/