I can neither upload nor download anything with the help of mozilla firefox 3.What should i do?

Example:
When i click the browse button near the upload field in websites.Nothing happens.

What should i do to get rid off it?
Don't tell me to use Internet Explorer because i want to repair this prob and not find sustitutes !!
Hope you will understand !!

Mine's doing that too; it's being a pain in the ass.