During one of the patch updates  in bug 1507595 an inexplicable change  slipped in that started trying to translate a function value explicitly annotated as not for translating. Most of the time it skips actually trying since usually the value is an array (of nodes) and it explicitly ignores arrays. But sometimes it's a plain text string which it'll try and treat as a fluent ID. When this is a long complex string like
wheel input enabled; scrollbar drag enabled; keyboard enabled; autoscroll enabled
it'll fail since
toFluentID() will reject it, but when it's the simple
none it'll try and retrieve a fluent string with the id "none" and log a missing strings error.
(Note: I haven't been able to reproduce this after writing up this bug, it's possible some since-
hg shelveed local changes to about:support were affecting timings in a way that caused it to manifest, but filing since the code still seems seems bogus anyway)
just below this comment, look for "Not localized"