Websites say that Firefox is outdated or incompatible even though it's the latest version https://support.mozilla.org/en-US/kb/websites-say-firefox-outdated-or-incompatible

This article is no longer maintained, so its content might be out of date.

https://support.mozilla.org/en-US/kb/how-reset-default-user-agent-firefox

http://www.howtogeek.com/113439/how-to-change-your-browsers-user-agent-without-installing-any-extensions/

Are you using NoScript?

• https://www.reddit.com/r/firefox/comments/9hdvyw/german_free_mailer_gmx_says_firefox_620_is/

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block (wanted) content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block (wanted) content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Firefox shows the shield icon at the left end of the location/address bar in case content is blocked by Tracking Protection.

• click the shield icon for more detail and possibly disable the protection
• You can check the Web Console by Tracking Protection
• "3-bar" menu button or Tools -> Web Developer
• https://support.mozilla.org/en-US/kb/tracking-protection-firefox

Thanks to you all, I tried it out, but did not get a result. So I will activate my thunderbird, visiting all the same the gmx site from time to time to prevent them from disactivating my account. It may be a combination of various factors - including my ubuntu version 18.04 lts.

Hello Peetra,

As you just now mentioned that you use Thunderbird, I will flag this thread and ask to move it to the Thunderbird support forum.

Mhm. Thunderbird is part of my solution, I did not use it before, so it is not part of the problem.

Would you take a look at this thread please :

https://www.reddit.com/r/firefox/comments/9hdvyw/german_free_mailer_gmx_says_firefox_620_is/