Firefox Android doesn't support opening multiple windows. This is available in other Chromium based browsers on Android (I've tested Vivaldi and seen it on Chrome for example), so it is possible.
Would love to see this change especially as with Android's upcoming desktop mode. I've been using it in beta for a couple months now and it's so incredible but definitely a bit held back by Firefox not being able to open multiple windows. If the feature exists and I just don't know how to find it, please share!
Of course, there are additional features that come with this like being able to drag tabs between windows, and plenty of other enhancements to the Firefox Android experience for large screens, but those can come later and I'm happy to share more details about them. 😁
