I always use the the go backwards and go forwards buttons on my mouse. Customizability is one of Firefox's features I love. I would like to remove the 'Go backwards one page' button and the 'Go forwards one page' button in the customise toolbar tab, which is currently not possible.
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Since the same functionality can be performed with a keyboard, 5-button mouse or mouse gestures, there is no reason to necessarily display back/forward buttons.
You know, most of search results that I did for your feature are an issue, in fact most of results are users telling that their arrows disappeared 😐. Maybe you can "perform" their same issue as for you it won't be an issue 🤣.
Allowing to remove these elements via about:config would be nice. And that would prevent accidentally removal via the context menu by non power users.