The browser extension opens up as a pop, and there is an option to detach popup as a separate window.
With some manipulation it is also possible to attach the detached window as browser tab.
To do this one need to
click + for adding new password
copy address from the uri1 field
it shall be something like “moz-extension://b8…”
paste that address in browser tab
It would be nice to have a button for openning popup in new tab. Maybe detach button, which is not used in detached version could attach popup/open as new tab?
Here is an issue about removing poopup button in popuped window: