Disable v3 extension blocklist for 10.0a6

https://bugzilla.mozilla.org/show_bug.cgi?id=1631018 landed and is enabling the v3 extension blocklist mechanism.

We are not sure how this effects our HTTPS-Everywhere extension. So, we disable that mechanism for now.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information