Possible email bug on Firefox 54 - updated

Yesterday I suddenly became unable to send email (using Earthlink Webmail on Firefox) from my destop iMac.  I had sent one at 0645, but by that afternoon it was no longer possible.  I could receive emails, and could read them, and I could write a message, but when I clicked the "send" button (or the reply button), the button greyed out without sending the message.  Other times the message was delivered to my "sent spam" (!) box.  I was also unable to save emails as a draft.

Interestingly, when I switched to my laptop (still using Earthlink webmail on Firefox), I could send emails normally.

This morning I found a possible explanation (though not yet a solution.)  This message was on Bugzilla@Mozilla:

Steps to reproduce: 1. Have an EarthLink email account. 2. Log in to (Earthlink Webmail). 3. Start writing a simple e-mail. 4. Either send or save a draft of it.

Actual results: Nothing happens. Webmail's "Send", "Save Draft", and "Cancel" buttons become gr(a/e)yed out.

I tried multiple accounts' addresses from two MacBook Pros (El Capitan v10.11.6 and Sierra v10.12.5) and a 64-bit W7 HPE SP1 machine. No problems in other updated web browsers (Chrome, Safari, and IE11) on the same machines. I downgraded back to Firefox v53.0.3 and retested. No problems!

And then this, also on Bugzilla@Mozilla:

We got a couple of user reports on sumo that sending emails from the earthlink webmail interface stopped working after the firefox 54 update & their support is apparently recommending a firefox downgrade as solution at the moment... They said there's an issue with the script on the submit button and that other buttons are still functioning normally. They suggested something has changed with the release of 54, I'll try to find out what exactly broke their script here. The web developer, who works on this is off but will give me a call back.

The same problem was logged in yesterday on the Firefox subreddit.

In my case, my desktop has been upgraded to Firefox54 (I'm set to upgrade automatically), but my laptop was still on Firefox53.  When I logged on to the laptop this morning, it started to automatically download Firefox 54, so I quickly went to Preferences and changed from "automatic" to "notify me and let me decide."

The solution may be for me uninstall 54 and reinstall 53.

Just FYI in case anyone else out there is using the same combo of Firefox and Earthlink.

Addendum just an hour later:
I tried switching from Firefox to Chrome, and was able to receive and send emails on Earthlink Webmail.  So the problem appears to have been with Firefox, not my computer.

And now the Firefox/Earthlink Webmail system is working again.  Without downloading any patches to anything.  I don't understand.  Maybe something was changed at some central location.  It's like the tide coming in and going out - you can't explain that.  Maybe the internet is no place for an English major...