Windows 7 might display a tiny thumbnail of a window when you hover your mouse over the Firefox tile on the Task Bar, but otherwise, minimize should not display the window at all.

Have you restarted Firefox and/or Windows since this happened?

Sometimes it's helpful to rename the settings file that stores the last window size and some other settings (e.g., toolbar customizations). If you would like to try this:

(1) Open your personal settings (AKA Firefox profile) folder

Help > Troubleshooting Information > "Show Folder" button

(2) Switch back to Firefox and exit the program (e.g., Firefox > Exit or File > Exit)

(3) Wait a few moments for Firefox to finish updating files in your settings folder, then rename localstore.rdf to something else, like localstore-bad.rdf or localstore.old. Alternately, you can delete the file.

(4) You're done with your profile folder and you can restart Firefox now.

Any luck?

Thank you for your reply. I haven't been able to find the FF profile folder

I had restarted windows and FF but I still got a window that filled my screen which makes it hard to have several windows open overlapping.

I went to troubleshooting and clicked on restore FF to its original state and that worked. I had to reinstall a couple of extensions I had but that was easy and my problem is solve.