Under Firefox Quantum 60.0.0, the expand to new window function does not work correctly. It opens a new window, but it's blank. Oddly, pressing F12 to open the FF web developer tools causes the new window to properly load. Toggling F12 again removes the web developer window to reveal the fully loaded pushbullet window. Nothing else works; the new window just remians blank unless you toggle the F12 on and off.
IUnfortunately, there is no apparent means of communicating this to the pushbullet team, other than a review. So, you get yet another 2 star review... Understand?