Try starting your pc in safe mode. See if that helps.

Hello nathanv, the issue might be caused by your Windows Firewall being turned off ! See the next article to fix that easily : [https://support.mozilla.org/en-US/kb/firefox-installer-crashes-windows-xp Firefox installer crashes on Windows XP] thank you

Start '''[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Firefox in Safe Mode]''' {web Link} by holding down the '''<Shift ''(Mac Options)'' >''' key, and then starting Firefox. Is the problem still there? Type '''about:preferences#advanced'''<Enter> in the address bar. Under '''Advanced,''' Select '''Network.''' Look for '''Configure How Firefox Connects''' and press the '''Settings''' button. Check the settings. ------------ Some problems occurs 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 '''[https://support.mozilla.org/en-US/kb/configure-firewalls-so-firefox-can-access-internet Configure firewalls so that Firefox can access the Internet.]''' {web link}