Fennec 95.2.0 (F-Droid build of Firefox/Android)
Checking Mozilla Support, this seems to have been a recently-restored capability as it is discussed as recently a 2021/1/10
It seems to have been restored by 2021/1/11
See issues #3710 #3972
https://support.mozilla.org/en-US/questions/1309515
From https://github.com/mozilla-mobile/fenix/issues/3710 it appears the (manually-entered "view-source" option) was restored by build 92.1.1, in a comment dated Sep 14, 2021.
From https://github.com/mozilla-mobile/fenix/issues/3972
Feature seems to have been restored to Nightly releases as of 27 May 2021, build 88.1.4
