When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

(1) Bypass Firefox's Cache

Use Ctrl+Shift+r to reload any specific page fresh from the server.

You also can clear Firefox's cache completely using:

orange Firefox button or Tools menu > Options > Advanced

On the Network mini-tab > Cached Web Content : "Clear Now"

This may take a few minutes depending your cache size.

(2) Remove your google.com cookies (save any pending work first) using either of these. While viewing a page on google.com:

• right-click and choose View Page Info > Security > "View Cookies"
• Alt+t (open the classic Tools menu) > Page Info > Security > "View Cookies"

Then try reloading the page. Does that help?

Since multiple computers are affected, might you have installed a privacy extension that is interfering with Google's scripts in some manner? You didn't list your extensions in your system information, so I'd be guessing if I listed any.

To review extensions:

orange Firefox button or classic Tools menu > Add-ons > Extensions category

Paste-able list:

Help > Troubleshooting Information

Which security software (firewall, anti-virus) do you have on those computers?

1. My browsers always run with an empty cache and no cookies. I use a script that clears everything on browser starting and closing.

2. I mentioned that I tried in "safe mode" (all extensions disabled) with the same effect.

3. Security: Norton. Those sites work in Chrome, so the firewall/antivirus are probably not the reason.

Could you test in a new Firefox profile? This would bypass your Firefox customizations, other than plugins.

Close Firefox and start up in the Profile Manager as described in Profile Manager - Create, remove or switch Firefox profiles. Any time you want to switch profiles, close Firefox and return to this dialog.

Note: I don't recommend deleting any profiles until you are 110% certain you do not need them.

Any difference? If the pages load fine in the new profile, you could compare the prefs.js file in the two profiles to see whether you can spot any relevant differences. (There will of course be numerous spurious differences that accumulate through use...) The quickest way to navigate to your currently active profile folder is:

Help > Troubleshooting Information > "Show Folder" button

Up a level to see all of the profile folders for the current Windows user.

I have three machines; each has a different profile. One machine, used for development, has a version of FF with no changes (customizations, extensions, whatever) from the installation defaults.

This is not a profile problem; all display the same behavior. Chrome works.

Did this problem begin with any particular event, such as updating to Firefox 18?

What does your script do to "clear everything" when Firefox starts up and shuts down?

Trying a new profile is a 3 minute experiment, but if you won't run it, that's your call. Would be better to try it after deactivating your script to rule that out as an issue.

Found the problem. All the systems had a registry entry in a Firefox Extensions key that referred to value name/data pairs in the Application Data folder. I didn't recognize one of the names, so I opened that folder. There were several .js files and several contained strings that referred to Google and other search engines.

I deleted the registry key entry and moved the folder (backing up the registry first, of course). Rebooted. Now FF works as it should.

Each FF installation was an upgrade of an old FF install. Maybe this was a surviving remnant of an old add-on; I had some really strange add-ons in FF's early life.

What was the name of that folder?

Was there also an install.rdf file in that folder?

The folder was in something like Application Data\Persistence\{'alpha-numeric-string'}. It had several files and folders in it.

The name "install.rdf" looks familiar, think one of those was there too. The folder contents looked similar to the files in a FF extension app installed through FF or an external program.

After everything was working I deleted the backups so I can't be certain about the names. (Emptied recycle bin.)