I see the article for Mozilla Firefox ESR, Portable Edition 68.9.0: https://portableapps.com/news/2020-06-03--firefox-portable-esr-68.9.0-re...
The download link in the article goes to the main page for Firefox ESR which (unfortunately for me) has the most recent version (78.6.0): https://portableapps.com/apps/internet/firefox-portable-esr
That main page does include a link for "Legacy versions" but that only includes v52 and v45: https://portableapps.com/apps/internet/firefox_portable/legacy
Since v52 has its own page I thought maybe 68 has its own orphaned page, but it does not: https://portableapps.com/apps/internet/firefox-portable-legacy-68
So... where could I find the download for Firefox ESR, Portable Edition 68.9.0?