Well, you genii, it works - although after initially getting a sniffy'this browser is unsupported' message with the Firefox/Mac string(which popped up even though the site subsequently appeared to work), Ihave gained access using a Safari string gained from BMX's Wiki link.
Greenies all round.
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Dang ... that 'unsupported' message keeps appearing, and the functionality of the web-based publisher is all mucked up. It's not telling me I'm not on a Mac and plain refusing to work, as it has in the past, but it is still misbehaving. Somehow Firefox for Mac must work in a different way to Firefox for Windoze, because I can use Firefox on the Mac without any problems.
Never mind, it was worth a go!