If you want two (or any number of) objects to be on the same plane, just group them. They will then line up together rather than on the sphere. You’ll notice when you group things, it shows a plane that encompasses the grouped items.
There’s a great tutorial on Groups and Layers here: https://www.youtube.com/watch?v=6u7XgbzlkUU
For the Firefox issues, I tried Firefox 78.02, and then upgraded to 79, I don’t see any of the issues you are referring to . I was able to resize normally in 78.02, and I attached an image of the tooltip from 79. Maybe just try restarting your browser?