So I come home from the Mythcon trip (more on the rest of that later) and turn on my computer to discover that Firefox has created a new updated version which is a complete tabula rasa. It doesn't include any of your logins, bookmarks, cookies, add-ons, display preferences, anything.
Panic. How do I get these things back? The new version welcome page indicates you can do this, but I follow the links and it takes me to a page where you sync your display with your smartphone. OK, but that's not what I was looking for.
After considerable searching, I find a help article which purports to explain how to do this. I find it confusing and hard to understand.
Eventually, having worked through this instruction and that, and comparing what I get here with what I get there, I come up with a much simpler answer.
1. Type "about:profiles" into your search box.
2. There will be two profiles. (Use the "root directory" versions only, not the "local directory.") For both, click on "open folder."
3. This will open up Windows file manager boxes for each. It should be obvious which one is the new directory (its file dates will all be today; the other one will have older dates, particularly if you last used Firefox a week ago before you left for Mythcon.)
4. Now that you have these open, close Firefox itself, because you are about to rock its world.
5. Make a copy of the new directory, just in case.
6. Copy all the files from the old directory to the new one. All of them. The help article doesn't want you to do this, because it doesn't want you to be able to preserve your add-ons or display preferences. Ignore this. Do it anyway.
7. Re-open Firefox. Presto, the new Firefox now has everything the old Firefox had.