Some add-ons or settings might change the information in the configuration database , that cause a problem in "downloading files" or "saving pages" . i.e. whenever you click on a download link and choose the option "save file as" , nothing happens .

The solution to this problem lies in resetting the values in the configuration page . ( That's what is cool about firefox being an open source program )

Open a new tab . Type about:config in the address bar .

Search for browser.download .

A list of values will appear . Right click and reset the values for all attributes .

Download in firefox will work fine now.