You are using a really old version of Firefox. The current version for me is 83.0 (64-bit).

Operating System: openSUSE Tumbleweed 20201213 KDE Plasma Version: 5.20.4 KDE Frameworks Version: 5.76.0 Qt Version: 5.15.2 Kernel Version: 5.9.14-1-default OS Type: 64-bit Processors: 8 × Intel® Core™ i7-4810MQ CPU @ 2.80GHz Memory: 31.0 GiB of RAM Graphics Processor: Mesa DRI Intel® HD Graphics 4600

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/

https://support.mozilla.org/en-US/kb/websites-say-firefox-outdated-or-incompatible

Do you have enabled "Resist Fingerprinting" if you check ‘’’Resist Fingerprinting’’’ on the ‘’’about:config’’’ page as this affects the user agent?

• privacy.resistFingerprinting = false
• https://support.mozilla.org/en-US/kb/firefox-protection-against-fingerprinting

Thank you to both people who replied to the question.

Obviously I did not make the question clear enough. The web sites concerned were right, the Firefox version on my computer is an old one. But in the Firefox set up it is stated that updates will be automatically incorporated as they become available. Am I right in thinking that statement applies to that particular version only, and that when a newer version becomes available you need to install that one ?

If you have trouble with the upgrade, use this link; http://www.mozilla.org/en-US/firefox/all/

I would like to know what distro you're running and why they are not updating Firefox.