Based on the screenshot that you've posted, it looks like you are not currently using the profile folder that you have moved to your D: drive. You appear to be using the default blank profile that Firefox creates.

Try pressing the Launch profile in new browser button and see if your data is in there. If it is, you need to set that as the new default profile.

Hope this helps.

Note that the OP wrote: But if I make the D Drive profile the default it looks like a new profile with no existing bookmarks/add ons

Did you try to copy only selected files to that profile on the D-dive or possibly rename the profile on the C-drive to make it impossible to access this profile ?

Even if the profile has the same name there are probably still files with an absolute path that reference to the original profile on the C-dive.

Thanks for your comments. I can now see that I had to copy the old location files (not folder) and paste onto the new location files. All good now.