Several planned code deprecations for Firefox 70, currently available on the Nightly pre-release channel, may impact extension and theme developers. Firefox 70 will be released on October 22, 2019.
Aliased theme properties to be removed
In Firefox 65, we started deprecating the aliased theme properties
headerURL. These properties will be removed in Firefox 70.
Themes listed on addons.mozilla.org (AMO) will be automatically updated to use supported properties. Most themes were updated back in April, but new themes have been created using the deprecated properties. If your theme is not listed on AMO, or if you are the developer of a dynamic theme, please update your theme’s manifest.json to use the supported properties.
accentcolor, please use
headerURL, please use
textcolor, please use
The Site Compatibility working group also intends to remove the non-standard prototype
uneval by the end of 2019.