I had minimized my Opera browser to resize it, but it disappeared. It didn't occur to me to right-click on the desktop and click side by side (lol). I open it and it's nowhere to be seen. The icon does appear on the taskbar and it doesn't give me the option to restore/maximize when I right-click it. I've uninstalled and re-installed it.
Try downloading CCleaner, then go to Custom Clean and check Window Size/Location Cache. if you don't want it to clean other items too, such as your browser history, recycle bin, etc, uncheck the options.