Hi

Can you just quickly check to see what is reported when you use this site?

If you copy what is report next to "rawUa" (the first item on the list) and paste into a reply to this thread it would be handy.

Could you check this article: How to reset the default user agent on Firefox.

This is what rawUa reported:

• rawUa: Mozilla/5.0 (Windows NT 6.1; rv:50.0) Gecko/20100101 Firefox/50.0

As for the "How to reset the default user agent on Firefox." article, I had already read it before posting the question and it did not work, but thank you for the help anyway.

Since you already tested in Firefox's Safe Mode and checked the useragent preferences:

Do you browse through any intermediaries such as a proxy server, security software filter, or private VPN that might be modifying the user agent string sent to websites?

You can check Firefox's connection setting here:

• Windows: "3-bar" menu button (or Tools menu) > Options
• Mac: "3-bar" menu button (or Firefox menu) > Preferences
• Linux: "3-bar" menu button (or Edit menu) > Preferences

In the left column, click Advanced. Then on the right side, with the "Network" mini-tab active, click the "Settings" button. The default of "Use system proxy settings" piggybacks on your Windows/IE "LAN" setting. "Auto-detect" can lead to a flaky connection. You may want to try "No proxy".

For external software or services, you probably have a better idea of what you're running than we do...

My Firefox network settings were already on "No proxy", I occasionally browse via a private VPN with the OpenVPN client, however it does not modify my useragent.

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.

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

After following the "To fix the problem in the original profile" instructions detailed in cor-el's second link, I found the problematic file to be prefs.js.

Creating a new profile would have solved the problem, but it's not an ideal solution. So I looked through every about:config value that I had modified and reset any that could possibly affect the useragent. I reset both

• browser.migration.version
• extensions.acr.previousApplicationVersion

but it made no difference.

Then I reset

• privacy.resistFingerprinting

from true to false. And it worked! My useragent was correct.

Although I'm not sure if this is the intended behaviour for "privacy.resistFingerprinting", surely the most common useragent of Firefox users would be the latest version of the Stable branch on Windows 10? Especially when the current behaviour prevents you from using AMO properly.

TL;DR: Set "privacy.resistFingerprinting" in about:config to false. Or delete prefs.js

Hmm, what a nightmare can flipping this pref cause:

• https://dxr.mozilla.org/mozilla-central/source/dom/base/Navigator.cpp
• https://dxr.mozilla.org/mozilla-central/search?q=regexp%3AresistFingerprinting

Thank you for reporting back on this.

"Barely Harry" said

Then I reset

• privacy.resistFingerprinting
  

from true to false. And it worked! My useragent was correct.

First, you can reset that preference using about:config in the usual way and Firefox should then update prefs.js:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste fing and pause while the list is filtered

(3) If the privacy.resistFingerprinting preference is bolded and "modified" to true, double-click it to restore the default value of false

Second, this should be added to the article about resetting your user agent or websites thinking you have an out of date Firefox.

Third, it would be useful to create an article on what this preference does. It may be that it's not really intended to be turned on yet and the documentation will come after it's better tested?