Hi, I returned my late 2016 i7 13" MBP for an i5 13". I restored a backup of the system (tried both Time Machine restore & SuperDuper) and this issue exists in both restores. I'm not sure if this was a problem prior to the restore, only noticed it after getting the new laptop. I installed Safari extensions (Adblock, Reddit Enhancement, 1Password) during my initial build without issue. After restoring the backup to the replacement laptop I noticed could no longer install Safari extensions. Clicking on the extension button in Safari takes me to https://safari-extensions.apple.com. The "install" link for all extensions is missing. I searched the net for days looking for solutions. I tried deleting the extension folder from Safari Library folder, then all Safari files from Library, didn't help. I tried deleting various certificates per other posts, also ineffective. I also reinstalled Sierra over the current install, no effect. I called Apple support twice, both times was told that 3rd party extensions aren't supported by Apple, despite it being an Apple page! When I told support that the "install" option was there, now it's missing, they said, "That's due to a recent Apple update, you now have to go to the developer website directly for extensions", clearly a lie because my 2015 Macbook sitting next to me still showed the "install" option. Both the person on the phone and another attempt for support via chat ended up abruptly disconnecting me when I questioned them why it worked a few days earlier and is still working on my other Macs. Eventually I found that by rebooting, clicking on the extension link that takes me to https://safari-extensions.apple.com, then deleting 'safari-' from the URL, and reloading the page would sometimes bring the "install" link back for extensions. Sometimes I need to do this multiple time or reboot several times and keep changing the URL before it works. A day or 2 later "install" disappears again and I have to go through the same process. Does anyone know what could be causing this and how to stop it from recurring? I'd hate to have to reinstall Sierra from scratch and spend days installing/configuring my apps but I would if that would resolve the issue. I'm not running any unusual software, everything on the Mac with the issue is installed & configured identically on my other Mac which has never had this issue. Could restoring the backup of an i7 13" to an i5 13" have caused some glitch in the OS? The stranger thing is how it keeps coming back. Thanks for your help!