The about:config issue is resolved.
I reset browser.places.importBookmarksHTML, and it is now gone.
Without a search, I was able to navigate to
File System > Home > my computer name > Mozilla > Firefox > hpde4zx.default > Bookmarkbackups
where the .json files are located.
The earlier search helped and I'm still learning, slowly.
It seems 5 of the last 7 JSON files were corrupted.
None of the entries that showed up in the Restore function were restorable, from the library.
I opened an older JSON file, in gedit.
I found a conversion site that converts json files to html, and works well:http://shancarter.com/data_converter/
I pasted the contents of the json file from gedit, into the box, and then pasted the conversion result into another tab in gedit. I then saved this file as: bookmarks 11-18-12.html
Then, I imported the html file and all of my bookmarks, from a much earlier date, were restored. So, the date on the json file is not accurate. At least the foundation is back.
I did move the bookmarks from the new toolbar at the bottom, to the top toolbar.
I don't know if that were necessary, but I did not want to delete the top toolbar. I was accustomed to the toolbar being near the top, so that was what I did.
Dell Inspiron 1521, AMD® Turion 64 X2 Dual-Core Mobile, ACPI x86-based PC, ATI Radeon® X1270 Graphics, DRAM bus width is dual-channel (2) 64-bit buses, Memory: 2048MB, Samsung HM160HI ATA Hard drive. Vista Home Premium, Linux Mint 9 boots first.