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Firefox has an "overflow" menu near the right end of the main toolbar, so when new buttons are added, they may end up on that list. You can use Customize to reorganize your buttons so the most important ones are on the visible part of the bar. https://support.mozilla.org/kb/customize-firefox-controls-buttons-and-toolbars
Some add-ons do not have a toolbar button, but instead integrate into a right-click context menu or have a keyboard shortcut. Usually their page on the Add-ons site will have a screenshot or text description of how to call up the add-on's functionality. Sometimes the button will be optional. You can go to the built-in Add-ons page (Ctrl+Shift+A, or on Mac, Command+Shift+A) and click into the Extensions list. Click an add-on's name to call up its Details panel, and check whether it has an Options / Settings / Preferences tab.
Hiding add ons are not good for some manual operations, video download helper (I want to chose the type that I want to download), adblock (I want to choose some of the irrelevant ads but can not use manually) as like this I also cannot add my favorite add ons to the toolbar. Until this issue is fixed, I am gonna have to use other browser, this is a must for me.
I don't want to use other browsers because this is my favorite one and I want you to fix this issue, please. And for the last two days, I haven't seen used the add ons properly because I don't think that they are working. Just check video download helper, adblock etc.