Warning: This workaround needs an add-on that is not actively monitored for security by Mozilla. Make sure you trust it before installing.

1. Install Open URL in Container addon.
2. Open bookmark manager by clicking on Main menu > Bookmarks > Manage bookmarks
3. Create a new bookmark by clicking on Organize > Add bookmark...
4. Enter a name for the new bookmark (e.g. Containerize a Bookmark)
5. Enter the following code snippet in URL:

javascript:(function(c,u){c&&(c=c.trim())&&(u=prompt('URL?',location))&&(u=u.trim())&&prompt('Contained URL to copy and bookmark:','ext+container:name='+encodeURIComponent(c)+'&url='+encodeURIComponent(u))})(prompt('Container name?','Personal'))

6. Add the bookmark in a place where you can click on it like the Bookmarks toolbar (Ctrl + B). Note that you can't launch a bookmarklet by searching for it in the address bar.
7. Go to the site you want to run in a specific container.
8. Click the bookmarklet you created, pick the container name and copy the link.
9. Create or edit some existing bookmark to set it to this link.

1. Type about:addons in the address bar
2. Click on the gear button over the extension list in the top-right corner
3. Click "Manage Extension Shortcuts"

1. Open Multi-Account Containers
2. Click on the info button in the top-right corner
3. In the addon preferences, edit the "Keyboard Shortcuts" section

Note: This also includes sites that have been checked to "Remember my decision for this site"

1. Open Multi-Account Containers
2. Click "Manage Containers"
3. Select the Container you wish to manage
4. Click "Manage site list" on the Container Edit panel
5. Click the trash can icon over the site you wish to remove

Windows SSO is disabled in containers by default (See bug 1800971). There's work in progress to add an option in about:preferences#containers. In the meantime, you can enable Windows SSO in a specific container by:

1. Get the container ID. this is available in containers.json in your Firefox profile directory, in a key called userContextId (47001 for example)
2. In about:config, create a boolean key named network.http.windows-sso.container-enabled.CONTAINERID, where CONTAINERID is the ID you found in containers.json, and set it to true