What's your computer system and Firefox version?

Some problems occur when your Internet security program was set to trust the previous version of Firefox, but no longer recognizes your updated version as trusted. Now how to fix the problem: To allow Firefox to connect to the Internet again;

• Make sure your Internet security software is up-to-date (i.e. you are running the latest version).
• Remove Firefox from your program's list of trusted or recognized programs. For detailed instructions, see

Configure firewalls so that Firefox can access the Internet. {web link}

Using Windows 7, can't see what version of Firefox because it won't open (but it should be the most current). Using Windows Firewall. Followed instructions above for configuring Firefox through firewall, nt working right away but will reboot computer and try again.

B.Regenwetter said

Using Windows 7, can't see what version of Firefox because it won't open (but it should be the most current). Using Windows Firewall. Followed instructions above for configuring Firefox through firewall, nt working right away but will reboot computer and try again.

After rebooting computer, Firefox still not starting.

Start your Computer in safe mode with networking. Then start Firefox. Try Safe websites. Is the problem still there?

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Rebooted in Safe Mode with Networking. Firefox will not start up at all.

EDIT: click on Firefox icon on Taskbar and it doesn't even register that I clicked on the icon. Tried opening by going to C:Program Files/Mozilla file and opening firefox.exe and that doesn't work.

Let’s do a full clean re-install; Download Firefox For All languages And Systems {web link} Save the file. Then Close Firefox.

Using your file browser, open the Programs Folder on your computer.

Windows: C:\Program Files C:\Program Files (x86)

Mac: Open the "Applications" folder.
https://support.mozilla.org/en-US/kb/how-download-and-install-firefox-mac

Linux: Check your user manual. If you installed Firefox with the distro-based package manager, you should use the same way to uninstall it - see Install Firefox on Linux. If you downloaded and installed the binary package from the Firefox download page, simply remove the folder Firefox in your home directory.

Do Not remove the profiles folder.

Look for, and rename any Mozilla or Firefox program folders by adding .old to them. Do not rename the Mozilla Thunderbird folder if there is one.

After rebooting the computer, run a registry scanner if you have one. Then run the installer. If all goes well, remove the OLD folders when you are done.

If there is a problem, start your Computer in safe mode and try again.

Starting The Computer In Safe Mode;
Free Online Encyclopedia

Followed instructions, re-installing worked. Rebooted a second time after installation and Firefox works as well as before. I even have my Bookmarks intact, so that's a bonus.

Thank you!

Hello,

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution more easily.

Thank you for contacting Mozilla Support.