What are some alternatives?
When comparing Open Tabs Next to Current and Firefox Multi-account Containers, you can also consider the following products
Tabs Outliner - Next Generation Session, Windows, Tabs Manager and a TooManyTabs Solution That Really Works.
Session Box - Using websites with multiple accounts at the same time is made easy.
Multiloginapp - Connect to websites as a multitude of different users
Tab Mix Plus - Tab Mix Plus enhances Firefox's tab browsing capabilities.
Multifox - Multifox is an extension that allows Firefox to connect to websites using different user names.
Tab Utilities - Tab Utilities is an ultimate tab solution for all kind of users who want to manage their tab, create multiple session and search for new tabs, etc.