Can't migrate profile
There is an "Old Firefox Data" folder on my desktop with all the data I need. I reinstalled Firefox and followed the instructions to copy the files from that folder into the "Local" folder (rather than root) for the new Firefox profile. I then restart Firefox. Have tried this several times and created new profiles etc. My old data is not showing up, even though the files are copied to the right folder. Copying the file into the folder doesn't have any effect.
ప్రత్యుత్తరాలన్నీ (1)
You need to copy the data to the Root Directory, not the Local Directory.
Naturally, I'm not sure exactly how you went about the process, so I'll describe the process that you want to do, just in case you've done it a different way.
You want to open Firefox and go to the about:profiles page in Firefox. If you have more than 1 profile listed (which is possible, if you've attempted to add new profiles), you want to find the one that says it's the profile in use.
Then you click the Open Folder button for the Root Directory. Once the window opens, you need to close Firefox. Assuming there's no data in your existing Firefox profile folder that you want save, you copy the contents of the Old Firefox Data folder into the folder that you opened from Firefox.
Hope this helps.