Others with similar problems please look at the article

• Firefox can't load websites but other browsers can

MM..,

mm... That just about sums up my thought on reading your question. Rather odd this one. I will list some brief ideas and number them to make them easier to refer to or comment on.

Obviously this does not affect all Firefox 27 on Windows 8. It must be something fairly specific to your setup. I have no idea what your problem is and you have tried some of the obvious troubleshooting steps.

Rather a general shotgun approach but the best I can do is suggest this list

1. Clean Install
   Presumably you will have tried deleting the program path files in order to get a clean install.
   Troubleshoot and diagnose Firefox problems_5-reinstall-firefox
   (See also note about ESR install)
2. Firefox SafeMode will also have been tried
   Diagnose Firefox issues using Troubleshoot Mode
   Remembering to disable or uninstall plugins, safemode does not do that.
3. Try a new clean additional test Profile.
   Profile Manager - Create, remove or switch Firefox profiles_creating-a-profile
4. Windows Safe Mode
5. Install and try Firefox ESR
   http://www.mozilla.org/en-US/firefox/organizations/
   • As a developer you are probably interested in using that anyhow.
     Either a customised install as an additional browser
     http://kb.mozillazine.org/Testing_pre-release_versions#Installing_multiple_versions
     Or use the unofficial Firefox portable. http://portableapps.com/apps/internet/firefox-portable-esr
   • Helps rule out: Firefox code or feature regressions, Corrupted program files
   • Should quickly enable you to see a working Firefox again
6. Run scans for malware problems with multiple tools
   • Troubleshoot Firefox issues caused by malware
7. Is it only network problems ?
   Confirm you are you able to open local html files on the same partition ?
8. Firefox's Network Console should throw light on the situation. There is also the Firefox Error Console and Profiler (Profiler is now built in)
   • https://developer.mozilla.org/en-US/docs/Performance/Profiling_with_the_Built-in_Profiler
   • https://developer.mozilla.org/en-US/docs/Tools/Network_Monitor
   • https://developer.mozilla.org/en-US/docs/Tools/Web_Console
9. also see kb.mozillazine.org/Standard_diagnostic

john99, thanks for the links. I went through them all (again), one by one. The last link kb.mozillazine.org/Standard_diagnostic showed me something that helped. I renamed "firefox.exe" to "firefox1.exe" and was able to use firefox.

That made me suspect firewall or malware. I ran a full scan from Malwarebytes, zero issues found. I have pored over the windows firewall entries, both the "Windows Firewall With Advanced Security" view and also the simple Control Panel view. The only mention of Firefox is the one I keep adding and removing to allow firefox through.

Wish I knew what was going on, but for now, I can at least use firefox. How frustrating!

It is possible that your security software (firewall, anti-virus) blocks or restricts Firefox or the plugin-container process without informing you, possibly after detecting changes (update) to the Firefox program.

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

• https://support.mozilla.org/kb/fix-problems-connecting-websites-after-updating

One possibility that may be worth looking into is that malware has changed properties of shortcuts.

• Does Firefox start ok if started using a run command firefox.exe
• Look for and check properties of all Firefox shortcuts.
• Look for any rogue executables that may be masquerading as Firerfox

Did you try as a test using additional profiles, maybe they work when created but corrupt later, if so what is being changed ?

On at least one machine install firefox ESR as an aditional browser. Ensure that has its own profile. Does that work ok ?

Did you look at the Firefox network console ? Did that throw any light on what is happening ?

An interesting thought, John, but running firefox.exe results in the same problem. There must be some stray "firefox.exe" in the windows firewall table somewhere.

FYI, this is still not working. I've just upgraded to 29.0.1 and I still have the problem.

First I uninstalled version 28.

Then I searched my windows registry under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SharedAccess\ and removed every occurrence of firefox.exe

Then I installed 29.0.1 and restarted.

Same problem. Firefox refuses to connect to any website, including http://127.0.0.1, localhost, or any internet address.

I turned OFF the windows firewall, and i still had the same problem.

But if I rename firefox.exe to firefox1.exe, it works.