When I get a book from Project Gutenberg, I usually download it in the plucker format, which PG now offers as an option. I find the chapter divisions and formatting are usually handled better in the plucker version.

If this format has been generated before, it's an immediate download. If you're the first, then you have to wait a half-minute while a pdb file is generated on-the-fly. Sometimes this process suggests an odd name for the file, or a name that ends in php (like a web page). Just give it the name you want, with that pdb extension.

OTOH, you can download the text or html version in a zip archive, and FBReader will read that file without your having to unzip it. And you can put a whole bunch of files into the zip if you want (have to add each one separately to your FBReader library, of course).

BTW, lots of ebooks have the extension pdb, but only some of them are Plucker format. Something to do with original Palm database format?

Also BTW, I've never encountered a book in FB2 format either, except when I went to a Russian site just so I could find one. To me, FBReader is a plucker/html/text reader.