1) Quit TenFourFox.
2) Delete (or move to the Desktop) the Firefox folder from
Macintosh HD>users>[your name]>Library>Application Support.
3) Go to
Macintosh HD>users>[your name]>Library>Caches and delete the Firefox folder.
4) Start TenFourFox.
If this doesn't help, re-download TenFourFox7450 and re-install it.
Cheers Chris. Carried out your suggestions. Alas, still getting the 'unable to connect' dialogue in the open tab, before and after a reinstall. Tried an earlier version 24.7.0 with same result. Safari 4.0.2 connecting fine, machine using ethernet to access internet, with an automatically configured IPv4 using DHCP. Would tenfourfox and safari's interaction with the systems network preferences be any different?
All good. Thanks. New user revealed an old version of a certain network monitoring app, which I thought I'd turned off, was running. Why it was blocking all outgoing connections from firefox... who knows.