Here's how I did it:
First, I started Basilisk and went to about:support. Next to "Profile folder," I clicked the button labeled "Open folder." Then I closed Basilisk.
Next, I went to FF 52.9 and did the same thing.
Then I copied everything from my FF profile folder into my Basilisk profile folder.
That took care of most of it, but upon reopening Basilisk and going to the about:addons page, some of my add-ons were listed as "Incompatible with Basilisk." To fix those, I had to open the "extensions" subfolder in my FF profile folder and drag the .xpi files for the "incompatible" add-ons from the extensions folder (some were in subfolders) and drop them on the about:addons page. This reinstalled and fixed the "incompatible" add-ons.