Firefox allows placing some less essential menu items to the overflow menu.
the menu icon highlighted in my browser:

the ‘remove from toolbar’ option is disable for this item:

I’ve removed all of the items from the said menu and only the ‘customise toolbar’ option remains — supposedly all entries (see the screenshot below) can be accessed from elsewhere and since extensions can’t be added to the menu, I’d prefer removing the icon entirely. This would save some horizontal space in the toolbar and make the keyboard navigation a bit snappier.

Firefox version 145. The related “extension button” has been customisable since Firefox 141.