I installed the update Mozilla Firefox 28. It was suppose to launch upon completion. it did not appear on the monitor screen, nor the task manager, but was running; for when I attempted to install the older version again it, it said that Firefox was running and needed to be turned off. I restarted the computer and tried opening Firefox, with the same results. After restarting again, I attempted to reinstall the update, with the same results taking place. I attempted to uninstall Firefox and install the new version. The same results took place. In the past, I could install Firefox 27 update, only now I can't for the same thing takes place. Past a certain version (19), this event takes place, but 19 and older can install it with no problems. I checked Firefox troubleshooting information. All was normal. I checked my firewall. Again, all was normal. Tried Firefox reset. Did not help. Tried with my firewall disabled. Did not solve the problem. Ran a virus check (deep) no viruses. Checked my computer system. No errors. I can install updates for my other programs, even install new programs; just not Firefox. What is going on and how does one fix it.