No Landscape Screenshots possible!

I want to take a screenshot of the whole screen. Unfortunately the page (a project tool) is completely displayed in landscape format (because of the timeline). For this reason Firefox can’t record the whole screen, because the existing tool only allows a vertical recording.
It is also not possible to do this manually. For the Firefox screenshot tool, the following is obviously true: “What happens to the left and right of the screen doesn’t matter”. It’s really annoying that it can’t do such a simple thing, because I find the tool quite practical.