The Reset Firefox feature can fix many issues by restoring Firefox to its factory default state while saving your essential information.
Note: This will cause you to lose any Extensions, Open websites, and some Preferences.

To Reset Firefox do the following:

1. Go to Firefox > Help > Troubleshooting Information.
2. Click the "Reset Firefox" button.
3. Firefox will close and reset. After Firefox is done, it will show a window with the information that is imported. Click Finish.
4. Firefox will open with all factory defaults applied.

Further information can be found in the Refresh Firefox - reset add-ons and settings article.

Did this fix your problems? Please report back to us!

Alas, I still couldn't add an attachment: I am able to browse to the file but won't attach and then it gets hung up so I am not even able to log out. :( I also use Microsoft Outlook for work emails and had no problem attaching files (nor when I used another browser , another :(

Some sites use a regular HTML form control to browser for local files, while other use a fancier Flash form control. In some cases, you have a choice in the site's settings to use one or the other. Is the problem site a popular one that a volunteer might have an account on?

jasher2000, Later in the day even in Microsoft Outlook, files would not attach... so, when all else fails, I rebooted the system, and so far, today, no problems! PTL, thanks for your help!