Re: well
"It works, it's just disabled on cellphones."
Quite. When I said it no longer worked I meant it was blocked. There was a period when you got the annoying message asking you to install the app but it would still let you through to the messages but that option disappeared eventually.
And your suggestion to try m.facebook.com gave me the idea to try using a non-default browser. It turns out that with the Opera Mini browser I can now access messages again via the web app.