Hope this gets continuous support.

Firstly, big thanks to the creator for this addon.

Secondly, I have to admit I don't use it in the intended way but rather as a workaround on sites attempting to block adblockers. Specifically Twitch. I don't know how it seems to work, but Twitch will block me from watching streams with an adblocker by giving me an error 90% of the time.

I started using this to circumvent it. For some reason, opening the stream in this side tab will FORCE streams to load in the main tab 100% of the time. Thank you, because without this I'd not be able to watch twitch with adblockers.

Для увеличения боковой панели
1. откройте about: config в Firefox и установите для параметра toolkit.legacyUserProfileCustomizations.stylesheets значение true
2. Меню Firefox -> Справка -> Информация для решения проблем -> Папка профиля -> Открыть папку, создаём папку Chrome
3. В папке Chrome создаём текстовый документ и вставляем в него текст
#sidebar-box {
max-width: none !important;
min-width: 0px !important;
}
Сохраняем и переименовываем в userChrome.css
4. Перезагружаем браузер и радуемся неограниченной регулировкой размера боковой панели.

I Love what this does. It is actually a very simple concept - but keeping your calendar or a cloud or mail acc handy on your sidebar shortens my workflows extremely.
I wish they would continue working on it, since I have seen that the last update was in 2018 :/

For any one want to remove the width limitation: https://superuser.com/questions/1276800/customize-the-maximum-width-of-the-firefox-sidebar

Very useful to the browsing experience, great addition to an already exceptional browser!

Remove the width limit and allow changing the zoom level on the sidebar please.