www/waterfox: Update 6.6.16.1 => 6.7.0-beta.3

First 6.7.0 beta moving Waterfox to the ESR 153 platform.

Release Notes:
https://www.waterfox.com/releases/6.7.0-beta.1/
https://www.waterfox.com/releases/6.7.0-beta.2/
https://www.waterfox.com/releases/6.7.0-beta.3/

PR: 297209
Sponsored by: UNIS Labs
MFH: 2026Q3

(cherry picked from commit 66176a33aca4cf06c82d140b93720aa5cadd4c0e)