Firefox doesn't normally have any problem loading CAPTCHAs. Do you know whether any of your content-blocking add-ons dislike CAPTCHAs?

I'm not sure what version you were using before, but since last year, Firefox does contain a feature that sometimes causes problems staying logged in. Firefox's "Total Cookie Protection" feature limits how sites can use "third party" or "cross-site" cookies, meaning cookies from different websites than the one you see in the address bar. Some sites pass you back and forth between different servers during login because they have their services spread out over a number of different servers. In those cases, you might be able to submit a form successfully on one page and then the next page says you are not logged in. Frustrating!

You can make exceptions to this feature when needed (for each server that you visit as part of the process of using this company's services). Try clicking the shield icon at the left end of the address bar (next to the lock). On the drop-down, click the blue slider switch to disable protection. Repeat on the site's other servers as you encounter them.

More info in the following articles:

• Introducing Total Cookie Protection in Standard Mode
• Total Cookie Protection and website breakage FAQ

Any difference?

Thanks! I accept all cookies. Made that change and restarted FF. No difference. BUT I restarted it with a virgin profile and was able to log in. Accordingly, it's GOT to be one of my extensions or something in the .css files. A few years ago I got rid of the extensions I could stand to lose (NOT happy about losing any of them, but over the years I've gotten used to it), so now I have to go through and cut stuff that really hurts. Problem not solved, just converted...

It would be nice if FF would leave the extensions in the list ordered by time instead of moving them around. It ought to be easier to keep track.

Disabled a lot of extensions and then removed cookies and site data with the little handbag (lock?)-shaped thing next to the URL, which solved the problem. I have batch-removed various cookies previously which caused me god knows how much trouble for weeks, so I regard cookie/cache clearing as something akin to suicide. I will try this with other problematical sites, so MAYBE this is a solution. If so I'll report back.

Worked with several other sites too. YAY!