Here's a very lightweight extension you can use in conjunction with built-in settings:
Click the icon to toggle the cookieBehavior preference, that's all it does.
When it enables cookies, it intentionally still disallows third party cookies unless you right-click the icon to toggle the thirdparty.sessionOnly preference (status will show in a tooltip when hovering over the icon).
This extension is primarily for people who like to keep cookies disabled unless it breaks a site, never want permanent third party cookies, and probably have the "Ask me every time" option selected to control exceptions like a whitelist (tip: that option is more bearable when you set the about:config pref network.cookie.alwaysAcceptSessionCookies to true for less repetitive prompting)
Bonus: Middle-click the icon to open your cookies list in a new tab.
Here's an existing per-site cookie settings tip (built-in to the browser) on any page:
right-click -> View Page Info
click on Permissions tab
view or change the Set Cookies options directly