Firefox has the containerization built in. You can use it without the extension but with worst UX.
> For advanced users: You can also enable Containers without the Multi-Account Containers extension, by changing some preferences in the Configuration Editor (about:config page). Note that you will get a better user experience by installing the extension but, if you choose not to, you can set privacy.userContext.enabled to true, privacy.userContext.ui.enabled to true and privacy.userContext.longPressBehavior to 2 in about:config.
> For advanced users: You can also enable Containers without the Multi-Account Containers extension, by changing some preferences in the Configuration Editor (about:config page). Note that you will get a better user experience by installing the extension but, if you choose not to, you can set privacy.userContext.enabled to true, privacy.userContext.ui.enabled to true and privacy.userContext.longPressBehavior to 2 in about:config.
https://support.mozilla.org/en-US/kb/containers