The big problem is that this happens from time to time without intention on my part. One way to activate tabs is to left-click on them. If that button is pressed to long and the mouse moved downwards just a bit it will move the website in the tab to the new window.

There is apparently no way of disabling the feature to drag and drop tabs into new windows in Firefox at this point. It happens about once a day that a tab gets accidentally dragged to much around so that it spawns in a new window. The only solution then is to copy the url, close the new web browser window, open a new tab and load the url again in the main browser window. It is not even possible to undo closing the tab in the main browser window as its history will be completely moved to the new browser window as well.

Please leave a comment if you know of a way to disable the spawning of new Firefox windows when dragging and dropping tabs.

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.

It is also possible to configure the left and top position of the window on the computer screen besides configuring the width and height of the window. It takes one click to change to the default screen resolution and two to change to any other defined in the add-on.

Custom Geometry is available at the Mozdev website. It is not compatible with Firefox 3.5x but can be forced so easily.