Edit…

I have finally found it for myself. If anyone is interested, it is done via Tools → Options → Security → Saved Passwords (which includes user names).

All solved.

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I am registered with both the mapping site and the forum using the same login name (ADCrawley), but Firefox insists on changing it to “adcrawley” in the mapping site which it will not accept. As I type the login name with ADC… it show a dropdown with both versions, but then always reverts to the all lower case version whichever one I select.

IE8 doesn’t make that change and logs in correctly, but I prefer Firefox for normal use.

Does anyone know how to stop Firefox from offering both versions?