User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:60.0) Gecko/20100101 Firefox/60.0 SeaMonkey/2.57

Steps to reproduce:

When I enter my YouTube-Subscription and channel pages they are blank. (On channel pages it often happens after some reloads)

Actual results:

Some days ago all YouTube pages went blank. (Videos played on a blank page)
On the next day the video-pages the YouTube start-page worked again, but my YouTube-Subscription and channel pages remains blank. This happens with the 2.53 branch as well as with the 2.57 branch.

When I switch the user agent to modern Firefox all pages go blank again (like on the first day when it happened)

tested with no active Ad-blocker on both builds.

Expected results:

Pages that aren't blank