[Osiris]

Source Resize The Firefox Window With Geometry

It is without doubt possible to resize the window of the Firefox web browser manually. This is usually the best way of doing so unless the user wants to resize the window to exact dimensions. This is for example useful for web developers who want to test websites in certain resolutions to ensure that the contents of the website are displaying correctly in all of them.
Another possibility are users who want to make sure that the Firefox web browser is not taking up more space than they want it to take which could be useful for systems with large computer monitors. Geometry is an add-on for the Firefox web browser that is adding the option to resize the Firefox window individually. The extension adds a button to the Firefox status bar that provides left-click access to the default window size configured in the add-on and right-click access to all other window sizes that have been defined by the user of the computer system.