Rated 5 out of 5 stars

For example, I have Stylish style for http;//example.com site. How I can modify my file in my preferred text editor? I don't want to create new style.

(And I don't find bugtracker for your addon.)

Thanks.

PS: @ChoGGi,
+ I set my text editor — http://i.imgur.com/Jnn7Hj1.png
+ I begin to edit my style → I don't find item for open file in external editor → http://i.imgur.com/EyY5XFm.png

Is it possible to realize behavior like in Greasemonkey? I open file in external editor → I edit and save file → I can to see my changes — http://i.imgur.com/yehC6Bn.png

Thanks, now all works for me!

This review is for a previous version of the add-on (0.8.7). 

You should be seeing changes as soon as you save the external file?
I've been working on 0.8.8, you can try and see if it helps
https://choggi.org/misc/Stylish-Custom/Stylish-Custom-0.8.8.3.xpi
https://choggi.org/misc/Stylish-Custom/change.log
The ID/Name is different so be aware; you'll need to disable the release version.

https://github.com/ChoGGi/Stylish-Custom


Edit: when you're in the style edit dialog; you'll need to manually add the external editor button (it's global for all styles once you add it)
rightclick and goto customize