I would like for us, users, to be given the power to customise the sidebar in the "customise toolbar" option. I think this will be useful should be added before sidebars are introduced into mainstream firefox. For example some users might not like the ai chatbot option. I have seen a lot of backlash against mozilla for adding that feature. I think they would be able to appreciate just going to the "customise toolbar" option just remove that button all together from the sidebar and follow "an out-of-sight-out-of mind" policy with it. I am not saying that it is a complete fix but whatever.
Also if you are implementing this just also add the ability to move the etensions addon to another place. Because if you are anyway going to mess with the "customise toolbar" option might as well just add it.