Tried to sync my extensions to a new computer, but some of them don't appear. It seems they have been officially taken down by Firefox. I tried to manually transfer the xpi file from one profile to the other but it says "this addon could not be installed because it appears to be corrupt". The new computer I'm trying to transfer the extensions is running Ubuntu and the old one Windows 10 (not sure if it was relevant, but anyways).

Thanks for your help.