Do you mean you want to remove the buttons completely, or you want to change from icons to text? (Recent discussion of icons-to-text and icons on the bookmarks toolbar: [https://support.mozilla.org/questions/1184828]) A lot of Firefox's interface can be modified using custom style rules. The more specific you can be about what you want to do, the better chance of getting rules that accomplish what you need. Sometimes this is not the best site for that kind of project because there are so many "emergencies." I have listed some alternate resources on the following page: https://www.userchrome.org/find-user-style-recipes.html