I had posted:
It wasn't backed up - will have to follow advice advice I've given
others ;/
I've not done file recovery since early days of WinXP.
On the affected machine I'm running Stretch(9.1) with Mate desktop.
The affected folders are on a partition normally mounted by a line
in fstab.
I immediately shut down.
There is another instance of Debian on a separate partition.
Logging in as root I edited fstab commenting out the appropriate line.
I feel the the data is still valid - there is just no appropriate
directory entries for the affected folder and its sub-directories.
I have copied the partition to another partition (using dd).
The critical data in the deleted folder(s) was my SeaMonkey profile.
I discovered I did have a several months old backup of the profile.
I am now running Squeeze (9.1) from a fresh install and installed the
latest SeaMonkey on it.
Several packages in the Debian repository have been suggested. I will
download their man-pages and will try them.
Several forensic packages have also been suggested which will used if
required.
Thanks for the help.