I have been using the new web beta editor for several weeks now. Love most of the new features thus far.
I am getting a green selection box that randomly appears. I am using Firefox ( up to date version ) on Window 10 ( fully updated ).
If I do a right click drag it will initiate this selection box but then it is difficult to get rid of. Sometimes it seems to just appear without me right click dragging.
Kind of annoying and gets in the way often enough. I have included a gif that show a brief demonstration if the issue.