With Firefox 42 and later it will no longer be possible to install addons not signed by mozilla
Firefox 42 may arrive in November 2015 ( https://wiki.mozilla.org/RapidRelease/Calendar )
This will affect both Fedora specific addons and private addons maintained by single users or some companies for the private/internal use. The only currently known ways to avoid loss of functionality is to have a developer or "unbranded" version.
Given the November date there may not be much time to loose.
Yes, so don't waste time and submit your unbranded package for review. See https://fedoraproject.org/wiki/Package_Review_Process for details. You can use pretty much the recent firefox package as a template, you just need to change name and remove the branding stuff.
Actually there's an unbranded Firefox package - https://apps.fedoraproject.org/packages/icecat - so you don't need to create anything and just use this one.
Anyway, new packages have to still keep processes for new packages so for any new package submission please follow the Fedora review process.