My question Does copying all cookie *.txt files from XP to Win7 work? is based on the mis-assumption that the .txt cookie files must have been generated by FireFox (see body text).
Thanks to the commenters that became clear.
Now what do I do - delete this question because it was based on an incorrect assumption, or leave it because there may still be value in the thread. I can imagine others may have the same confusion.
Maybe add an answer?