Did you check the permissions in "Tools -> Page Info -> Permissions" and in "Settings -> Privacy & Security -> Permissions" ?

• https://support.mozilla.org/en-US/kb/push-notifications-firefox

You can see all registered service workers on these pages:

• about:serviceworkers
• about:debugging#workers

You can check WebSockets via this page:

• about:networking#websockets

Did you check the permissions in "Tools -> Page Info -> Permissions" and in "Settings -> Privacy & Security -> Permissions" ?

• https://support.mozilla.org/en-US/kb/push-notifications-firefox

You can see all registered service workers on these pages:

• about:serviceworkers
• about:debugging#workers

You can check WebSockets via this page:

• about:networking#websockets

Thank you for your reply. I did check "Settings -> Privacy & Security -> Permissions" earlier, notifications are allowed for https://mail.google.com. Now I checked "Tools -> Page Info -> Permissions", and it says "Allow" under "Send notifications". Gmail is a registered service worker, but I don't see anything in websockets.

Did you contact Gmail support about notifications actions as that would be the first place to see what changed or what their instructions are.

Thank you for your reply. I did not contact them yet, but I will contact them.

Update:

After testing it again it... just started working. I did not change anything, and last time I tested it the notifications didn't work. I have no idea what happened, but at least it works. Thank you all for the replies. I will mark this as solved.