[direct commit] www/firefox: unbreak after r540842

r532707 is not in 2020Q2 but 2020Q3 ETA in ~1 day, so use bundled ICU.
https://hg.mozilla.org/releases/mozilla-release/rev/61970f5454db

> firefox-78.0_2,1 depends on package: icu>=67.1,1 - not found

> Installing existing package /packages/All/icu-66.1,1.txz

[121amd64-quarterly-job-12] Installing icu-66.1,1...
[121amd64-quarterly-job-12] Extracting icu-66.1,1: .......... done

> firefox-78.0_2,1 depends on package: icu>=67.1,1 - not found

• Error code 1

Reported by: pkg-fallout
Approved by: ports-secteam blanket