I made a personal theme in firefox color and I exported it into my computer as a json file for editing it (I added a background color to the new tab page).
Now I want to bring it back to my browser so I can use it.
What should I do?
*I do not want to publish it in Firefox add-ons page.
Hey @pugo! You will want to package the files (your edited manifest.json and any other files that were exported from Firefox Color) and then either sideload it to Firefox or upload it to addons.mozilla.org as a self-distributed add-on and then install the .xpi file. If you self-distribute the extension, it won’t be publicly listed on the Firefox add-ons site.
Thanks, it worked!
now I have another question:
when I entered to the debugging page ( about:debugging#addons )
I saw this errors:
what do I need to change to fix it?
Glad sideloading worked! 
You will need to edit the manifest.json and replace the properties flagged for deprecation with the recommended property, like:
theme.colors.textcolor with themes.colors.tab_background_text
theme.colors.toolbar_text with theme.colors.bookmark_text
Then re-zip and sideload.
Ok, I fixed it. now I have another question…
What does strict_min_version means?
And what should I write there?
Thank a lot for your support!
Happy to help!
strict_min_version sets the lowest version of Firefox your theme will work with. You shouldn’t have to worry too much about this because you’re not sharing your theme with other people who may be using out-of-date versions of Firefox, though you should be safe if you set it to 42.
There’s more information on MDN if you’d like to take a look.