DRDR said

I use Firefox as my browser with GMAIL; this separates the mail into Primary, Promotions and Forums buckets. This has always worked perfectly till recently. Mail seems to disappear from those categories. They are not in the Spam, Trash or under any label that I can find either. I recently discovered that the mail does still exist and can be seen only by selecting ALL Mail, where it will appear with no INBOX (or any other label). The only reason that I suspect this to be a Firefox problem is because this condition only seems to have occurred since updating to Firefox 39. Any advice would be appreciated.

Did you check it with some other browser? as the the mail disappearance might have nothing to do with browsers and are on server side.As you said it doesnt have labels mentioned.Did you check the settings for label filters or message filters in your settings?.Please let me know of this.I can definitely help you out. :)

Thanks Premm, I have checked for filters, there are none set. Re your comment about using other browsers. I keep my mail on the GMAIL server, however from time to time I use the Mac mail system to download it to my pc. This is very infrequent. Could that be it. Another possibility was that there was a new GMAIL version released. I tried it for a matter of minutes before reverting to the old system.

DRDR,

You didn't actually answer premm's question about whether you tried this in another browser. Of course we're glad you are using Firefox but can you test this in Google Chrome or Internet Explorer?

It is a known fact that the Mac Mail system interferes with the proper function of Gmail. Apple and Gmail do not have the same notion of what Archive or Delete means.

The new Gmail system launched a few months ago would not delete your messages. It is just an alternative way of viewing the contents of your inbox.

Tony98, You are right, I was not thinking straight. Although, as I said, I mainly use the Mac for mail administration (using Firefox), I still have a Windows machine used occasionally, but still under Firefox though. You have also brought to mind the fact that we also have Kindles and an IPAD, all of which we use to access the mail. With the IPAD I get into Gmail via a GMAIL app, but I assume it uses Safari? The Kindles use Silk. I can see that this is all far more complicated than I thought.

And just to keep things in perspective, you seem to be doing two different things with the Mac.

You said:

1. I use the Mac mail system to download it to my pc.
2. I mainly use the Mac for mail administration (using Firefox),

The first one is an email client program on your computer, which interacts with what's stored in your account on the web. The second one is simply using Firefox as your web browser on the Mac to sign in to Gmail.

Due to the way Macs are set up, many new users configure that first option without even realizing what they're using to get their mail, thinking it is actually a web browser.

When you've eliminated all the other issues, please let us know if you still need help with your Firefox browser.