Downloaded and installed Firefox last fall on new Mac Air, OS 10.9.5. Installed as directed, same way I have always done. When I dragged the icon to the dock, it seemed fine, but next time I used the Mac, it appeared as a '?', not the actual icon. Every time I click on the 'icon' in the dock, I get a bar " Verifying ". When it finished, I get the Mac window warning me it was downloaded from the net, do I want to open it ? I MUST click on 'open ' to get Firefox to run. Then it shows me the 'Install firefox ' window. So I have to go through install again, drag into application folder. I get another window telling me I am trying install an old version. Do I want to replace the one I have, keep both or cancel. I cancel. I can eject the disk and use Firefox after this. But every time I quit Firefox, close the Mac or Restart, I get to do this all over again. Every single time. VERY frustrating. Have installed all updates as they come along, so far has made no change to this nonsense. Used it on my old Mac for a decade with no problems, now this ? I just saw there is yet another update past my version of 31.0, I will install that, but no other updates have fixed this issue so far.