1) Install Stylish
2) Click 'Create New Style'
3) Add domain, copy-paste CSS, should look like this
CSS:

a, a:hover {
color: #4f8822;
}
a.chapter-read > i {
color: #4f8822 !important;
}

5) Save it. Close it.
6) Viola, it works. Some links may not update due to caching - Ctrl+F5 aka cache refresh should fix that

6252013
Thanks for the explanation

If you install Fimfiction 3.0 - Classic Green Navbar from stylish itself you get also back the green main bar at the top