OS X :: Window Stuck On Screen?

i had firefox open and i was typing on another site. i opened the special characters window because i needed a unique symbol. when i tried closing that window, it froze. i proceeded to quit firefox so it would go away. it stayed on my screen though, even with firefox closed. next i thought my computer was just being buggy. so, i completely shut it down for a while and logged back on. the window is still there and won't go away.

here's a screenshot i took so you can visually see what's going on here: [URL}

after the previous attempts didn't work i've tried completely removing firefox from my computer and redownloading it, which didn't work, and restoring my system, which also didn't work.