Excel Copy & Paste not working for me either!
Have you resolved this issue yet?? I'm having the same problem.... I'm not using Firefox - I use Google Chrome, (have recently changed from Internet Explorer to that). I also have Skype so maybe have that Skype Plug-in problem but have no idea how to find out...!!!
I use spreadsheets on a daily basis with formulas and I have been finding that instead of copying and pasting a formula, I have to type it in every cell because the copy and paste only pastes the value as a constant. When I do a copy and paste special, I get a weird screen that asks about the Source, and I can select Unicode text or text!!
If you have a solution, please let me know as this is driving me nuts too!!