Comment # 34 on bug 1221531 from Paul Tannington

(In reply to Pedro Monreal Gonzalez from comment #31)
> The DEFAULT policy in crypto-policies does not allow SHA-1 signatures but
> the LEGACY one does allow it. Could somebody test if switching to LEGACY
> helps?:
> 
>   > sudo update-crypto-policies --set LEGACY
> 
> Note that, this command is shipped by the crypto-policies-scripts package.
> 
> If it help, I would force using the LEGACY policy only in mozilla-nss by
> default for now in crypto-policies and submit in a moment.
> 
> TIA

Using a new Firefox profile with "update-crypto-policies" unchanged:
Unable to install extension "Installation aborted because the add-on appears to
be corrupt."

Using a new Firefox profile after "update-crypto-policies --set LEGACY":
extensions install correctly.

Using a new Firefox profile after resetting crypto policy
"update-crypto-policies --set DEFAULT":
Unable to install extension "Installation aborted because the add-on appears to
be corrupt."