I succeeded with an existing profile by deleting the file
extensions.json from iceweasels profile directory. All system-wide
installed add ons were detected without error, but all user installed
add ons had to be confirmed on the first startup.
Changing the setting of xpinstall.signatures.required was not required,
it is still in its default setting ("true").
You probably should check if you need to migrate this file on upgrades
to iceweasel 43+, since old profiles would refuse to work with the
system wide installed add ons, once iceweasel 44 would be released.
Ingo
--
╭─╮ Kennedy's Lemma:
╭│───╮ If you can parse Perl, you can solve the Halting Problem.
│╰─│─╯
╰──╯ http://www.perlmonks.org/?node_id=663393
