Try checking for a site-specific setting here:

orange Firefox button or classic Tools menu > Options > Privacy

If you have Firefox set to "use custom settings for history" click the Exceptions button to check for any google.com or www.google.com entries.

If you do not have Firefox set to "use custom settings for history" go ahead and select that temporarily to provide access to the dialog.

In addition to built-in features, some add-ons or external software could block cookies. Do you have any privacy-related add-ons here that might be relevant:

orange Firefox button or classic Tools menu > Add-ons > Extensions category

You could try disabling them temporarily, or check for any Google-related preferences.

What if I have completely uninstalled and reinstalled Firefox? I've cleared caches and cookies, there's nothing on the Exceptions list under "use custom settings for history," it was working all day and every day for as long as I've had the machine, and then all of a sudden I started getting the "cookie functionality turned off" message and not a single thing I do will work.

I freelance in another country and this is the only way any clients have to reach me. Does anyone have any idea how to overcome this?

Hi nandibrown, what is your general cookie setting? For example, I use

[X] Accept cookies from sites
[X] Accept third party cookies
Keep until: I close Firefox

Is your setting at least that permissive?

Also, check out the following reply in a different thread about manually deleting the cookies file in case it is corrupted: https://support.mozilla.org/en-US/questions/943218#answer-385398

Hi There,

Thanks so much for getting back to me. Yes, all three of those boxes are checked. Literally nothing changed between when everything was working, which has been for months, and when it all of a sudden stopped, which was earlier today. I just suddenly couldn't do anything or open either account. Now I can open my regular Gmail account at least occasionally, but everything takes about a year and a half and just says Still working...; I still can't open the work account at all.

I don't know what I was supposed to see when I clicked Show Folder, but I tried to follow the instructions at the link about corrupted cookies and neither of the two files I was supposed to be looking for were anywhere on the screen, so I couldn't delete them. The whole thing is just inexplicable and I'm helpless.

Thanks again.

Well. For lack of any other options, I tried reconnecting my work account to my main personal account, and both seemed to work. I sent a test message to the work account just to make sure it was receiving messages in real time, and then I closed and reopened Firefox to make sure it wasn't a fluke. I don't know what I did, but it seems to be okay now. Thank you very much for your help.