Feature: Import and edit using public exisiting theme #1083

There are tons of themes that user can download and use in Firefox. I just try to edit my theme to have new vibe. I dont have any art background so using existing theme helps me alot. But there is always minor issue with each theme and from there I plan to import the theme and edit it myself in Firefox Color. Turns out you cannot even import it, let alone edit it. What i mean by editing is just import and modify, when user export it, it is counted as different theme.

I am a programmer myself so if possible, I would like to contribute to Firefox Color to develop this feature.