Follow mozilla Bug 1778684, or other upstream changes to the toolbar extension buttons.
As part of #41581 (closed), we modified the mozilla extension code to:
- Hide the NoScript toolbar button by default, from the toolbar and the unified extensions panel (controllable through a preference "extensions.hideNoScript" with UI).
- Hide the unified-exetnsions-button if it's panel is empty (controllable through hidden preference "extensions.hideUnifiedWhenEmpty").
This is implemented in ddd31383 from !816 (merged).
The latter feature has a related upstream bug: Bug 1778684. It hasn't been implemented and looks like it might never be at the time of writing, but we should check its progress at the next ESR.
Moreover, there is an upstream meta-bug: Bug 1777480. This might influence this area, or stop our hacks from working.