Ever notice sometimes you right-click on a link and open a new window and it's not full screen? This usually occurs because IE remembers the last window size when closed. Many times a background pop-up will do this too, if it is the last window closed. To resize the window and regain control:

• Close all instances of Internet Explorer except for one.
• Right-click on a link in the page and select: "Open in New Window"
• Close the first browser window using the [ X ] (upper right corner)
• Resize the window manually by dragging the sides to the desired size.
  Note: Do NOT click the Maximize button, you must do it manually.
• Hold down the Ctrl key and click the Close button (upper right)

[Exception]
In some cases the "Remember last window size" info becomes corrupted in the Registry.

[HKEY_CURRENT_USER\Software\Microsoft\Internet Explorer\Main]
"Window_Placement"=
To reset the "Window_Placement" entry to default. You can download a small reg file to reset (to default) and correct this behavior.
Download: ResetWindowPlacement.reg [right-click and select: "Save Target As"]
To use: right-click and select: Merge - Ok the prompt and reboot.