Addons not putting button on toolbar

Hello all, I have not posted a question here for a while, but I am trying to add an addon to my browser to download videos, but none of them will put a button on the toolbar, so there is no way to use the addons once they are installed. So, I try '''Customize''' toolbar from settings, but they do not seem to show up there either. It is like they were never installed at all, and confusing me. I do have one addon for downloading videos, but I was trying to get a second one, and the browser will not let me, for some reason. Am I doing something wrong here, because I got the addons from the official Firefox addons site?? Is this a problem with the addons, or something stupid wrong with the browser, please clarify, and '''Thanks in advance!!'''