Simply awful. Tl;dr get PocketBook. FBreader is a sluggish reader. It requires a plugin to read pdf files  the documents list is awkward to use and doesn't remember the last location of the currently opened document. You have to navigate back to the folder if you are trying out a lot of ebooks. When zooming a page  navigating to the next page results in the view jumping to the portion that was previously outside the screen size.This is simply awful UX. A lot of functions have to be accessed by going into the menu.Quirky!
April 04 2016