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}

Maybe that's true but it is not at all relevant to my case. Thanks anyway.

rfalkowitz said

Maybe that's true but it is not at all relevant to my case. Thanks anyway.

Dismissing help doesn't give much for help.

rfalkowitz said

Following the upgrade of Firefox to version 67 running on Ubuntu 16.04, no site can be displayed. All of those sites can be displayed via Chrome. Disabling plugins and addons has no effect on this. Rebooting the computer has no effect. There were no error messages during the upgrade. Is this a problem with my configuration? With my installation? A bug in Firefox?

Are you using the package build provided from Ubuntu or the official build from Mozilla as in www.mozilla.org/firefox/all/

WestEnd said

rfalkowitz said

Maybe that's true but it is not at all relevant to my case. Thanks anyway.

Dismissing help doesn't give much for help.

Well it is not relevant as Fred's reply was more for Windows and not on Linux, as Ubuntu is a Linux distro.

You can check the connection settings.

• Options/Preferences -> General -> Network: Connection -> Settings

If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.

See "Firefox connection settings":

• https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

You can check the Network Monitor to see if content is blocked or otherwise fails to load.

• https://developer.mozilla.org/en-US/Tools/Network_Monitor

If necessary use "Ctrl+F5" or "Ctrl+Shift+R" (Mac: Command+Shift+R) to reload the page and bypass the cache to generate a fresh log.

See also the DNS Lookup tool on about:networking.

Seems like it may be a issue with the package build from Ubuntu and not the official build of Firefox for Linux from say www.mozilla.org/firefox/all

This poster /questions/1259828 had this issue with Ubuntu build but not with Mozilla build of Firefox.

I downloaded the version directly from firefox and installed it in my home directory and ran it. The behavior was identical. So I assume that the package itself from Ubuntu is not the problem.

cor-el said

You can check the connection settings.

• Options/Preferences -> General -> Network: Connection -> Settings

If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly. See "Firefox connection settings":

• https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can

You can check the Network Monitor to see if content is blocked or otherwise fails to load.

• https://developer.mozilla.org/en-US/Tools/Network_Monitor

If necessary use "Ctrl+F5" or "Ctrl+Shift+R" (Mac: Command+Shift+R) to reload the page and bypass the cache to generate a fresh log. See also the DNS Lookup tool on about:networking.

I cleared the cache - no change to behavior. I opened the network monitor. What I see is: a) the message, "Waiting for <server name>..." b) one line in the monitor for the GET, with no status and just the domain, file and cause, but no other information on that line.

This is the same, no matter what page I try to load.

I don't use a proxy. The preferences had been set to "User system proxy settings" (for which there are none). I changed that to "No proxy", with no change in behavior

Try to rename/remove prefs.js in the Firefox profile folder with Firefox closed.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Directory:
  Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder
• http://kb.mozillazine.org/Profile_folder_-_Firefox

You can create a new profile to test if your current profile is causing the problem.

See "Creating a profile":

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles
• http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues

If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems.

• https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile

Renaming pref.js did not solve the problem.

In the end I entered about:support, then tried running in safe mode. That worked. I was surprised by this, given that I had previously disabled all plugins and extensions. Anyway, I then did a refresh of Firefox.

Unfortunately, this method did not allow me to determine what, precisely, was causing the problem