v2.1

Release version 2.1

Changelog

    Update: target PDF.js version 2.13
    Add themes: Nord and Firefox reader view
    Revamp UI: neat, minimal & simplified toolbar
    Feature: separate preferences based on OS theme
    Feature: configurable options to control behaviour
    Improvement: accessibility and color schemes
    Improvement: better performance when reader is off
    Fix: printing, thumbnails & some minor errors