This could be a problem with the TLS 1.3 Early Data feature also known as Zero Round Trip Time Resumption (0rtt). You can try to set security.tls.enable_0rtt_data = false on the about:config page to disable this feature until this is fixed by Google or Mozilla to see if that helps.

See also:

• /questions/1376015 Issue with most Google sites on Firefox v100 64bit

Thank you. I have disabled the feature as you described. As I cannot reproduce the problem, only time will tell if this helped. I shall get back should this tweak not help.

I'm curious, are you running Firefox in compatibility mode as the possible cause for the tagging a Windows 7 ?

Check that you do not run Firefox in compatibility mode. You can open the Properties of the Firefox desktop shortcut via the right-click context menu and check the "Compatibility" tab. Make sure that all items are deselected in the "Compatibility" tab of the Properties window.

No compatibility mode. I genuinely run Windows 7. Thus I may encounter problems that don't happen with Windows 10.

This could be a problem with the TLS 1.3 Early Data feature also known as Zero Round Trip Time Resumption (0rtt). You can try to set security.tls.enable_0rtt_data = false on the about:config page to disable this feature until this is fixed by Google or Mozilla to see if that helps. See also:

• /questions/1376015 Issue with most Google sites on Firefox v100 64bit

Hello. That setting did not help. I experience a different problem/bug. And today I noticed this important detail in the dev console (see image). It seems that the DevTools cause this issue. After this happened Gmail could not be loaded in a new tab at all.

"Blocked by DevTools" can be a placeholder used in cases where it isn't clear for what reason a request is blocked.

• 1603805 - Decide how to surface the "unknown reason" blocked case in the UI

(please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html)

Thanks for your effort. But it does not help me. That bug report has low priority and nobody is working on it.

I seriously doubt that my Windows 7 is to blame. But frankly, can you tell if Firefox is officially supported on it or not? You know, the OS still has extended support from MS.

I am sorry but this bug is driving me insane. Tonight I tried to repond to an email. Everything looked fine. Until I clicked on the send button. Then the bug surfaced to UI again. I had to restart Fifefox, type master password, login again here and there create my email anew...