Update README.md
New preference icons
New icons for bookmark menu
Update all icons for Library View
Many new icons for about:addons

After working for 7 continuous hours, they are finally here!! (very
sleepy…)
Rename extension icon
Specify favicon for about:addons page

I want to remove it, but I can’t
Remake language pack icons
Remake all plugin icons
Update icons
Continue updating icons
Update question, warning and information icons
Move OS-specific code to the end of browser.css
Import css
Update README.md