Again, why allow addons to be packaged at all if we are not prepared to
block browser updates that break addons?
Alternatively, rather than block the updates, at least leave the last
working version in the repository so that users can downgrade to
something more recent. Right now it looks like F26 users can either
accept Firefox 57 and live without their addons, or downgrade to 54;
why not continue making 56 available for users who want it? As far as
I know DNF is capable of handling such scenarios, although maybe there
are other parts of the infrastructure that make this difficult.
In any case, maybe it is worth revisiting some of the relevant policies
on Fedora packaging. This is not a Firefox-specific issue; GNOME,
Emacs, etc. also have packaged addons.