https://support.mozilla.com/en-US/kb/Installing+Firefox+on+Windows

What kind of problems do you have with installing Firefox?

Also make sure that your security software is blocking the installation or the functioning of Firefox.

Remove all rules for Firefox and the plugin-container from the permissions list in the firewall and let your firewall ask again for permission to get full unrestricted access to internet for Firefox and the plugin-container process and the updater process.

See:

• https://support.mozilla.org/kb/Firewalls
• https://support.mozilla.org/kb/Server+not+found

• http://kb.mozillazine.org/Browser_will_not_start_up
• http://kb.mozillazine.org/Error_loading_websites

Clear the cache and the cookies from sites that cause problems.

"Clear the Cache":

• Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now"

"Remove Cookies" from sites causing problems:

• Tools > Options > Privacy > Cookies: "Show Cookies"

• http://kb.mozillazine.org/Cookies
• http://kb.mozillazine.org/The_page_is_not_redirecting_properly

Start Firefox in Safe Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.org/kb/Safe+Mode

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes