Steps to reproduce:

Open a blank tab
Enter calendar.google.com

Actual results:

Nothing loads

Expected results:

Google Calendar should be opened

This is happening on a few pages, not just Google Calendar. It is hard to figure out what is going on as I can't see any error in console, the page just doesn't load.

I have attached a video of the bug in action.

The Bugbug bot thinks this bug should belong to the 'DevTools::Console' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.

Does the problem still happen if you start Firefox in Safe Mode? (Safe Mode disables add-ons, extensions and themes, hardware acceleration and some JavaScript stuff in order to exclude some possible reasons for problems.) See https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode
And does this also happen with a new and empty profile? See https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems#w_6-create-a-new-firefox-profile

Thanks for the debugging steps.

I can confirm that the problem persists in troubleshoot mode and also in a newly created profile.
Some websites load, some don't, it's not consistent.
I enter the URL, hit Enter and nothing happens. I see some network calls being made but no responses.
Here's another video I took in a newly created profile

Hi, could you try to capture a http log for this?
Thanks.

Here are my HTTP logs

I would like to add that Chrome and Edge are working perfectly, it is just FF that I am encountering this issue with.

Thanks for the log.
Looks like this is a dup of bug 1768250. Both logs show that 0RTT is related.

I can confirm the problem is gone for me after disabling security.tls.enable_0rtt_data
Also, I have Sophos installed