In Early Bird in Opera GX, you can enable "Guest tabs". Basically, you can right-click on a tab for a page and choose to open it up in a guest tab that will open the page in another session (so you can log in with a different account for that site for example). The downside is that all guest tabs share the same session, so it will only give you one extra session for a site/page, no matter how many times you open it up in a guest tab.