I checked the Firefox Accounts, Push, Sync, and Token services for compatibility with the proposed TLS ciphers/protocols and all four support every cipher proposed and TLSv1.2.
Bug 1537701 Comment 12 Edit History
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I checked the Firefox Accounts, Push, Sync, and Token services for compatibility with the proposed TLS ciphers/protocols and all four support all the AES ciphers and TLSv1.2. When services migrate over to GCP they'll be able to use the ChaCha20-Poly1305 ciphers.