www/firefox: update to 136.0 (rc1)

Release Notes (soon):

https://www.mozilla.org/en-US/firefox/136.0/releasenotes/

Switches to bundles ICU, because the one in 2025Q1 is too old and
the uplift would be too messy.

While here, catch up with previously unmerged change bf57fa930359

(cherry picked from commit c1a1b28d9f494603f1036e421234bbd3b7594829)