See the previous post for the detail. We tested the new behavior with a lot of assertions in the editor and I've fixed a lot of issues for 3 months (Thank you for the Fuzzing team!).
I think that now we can ship the new behavior in the all channels.
Bug: Bug 1858071 - Enable `editor.block_inline_check.use_computed_style` by default in all channels
Specification: None
Platform coverage: All platforms
Preference: editor.block_inline_check.use_computed_style
Other browsers: Both of them use the new behavior
web-platform-tests: editing/other/insertparagraph-with-white-space-style.tentative.html and the tests whose manifests are touched by the patch.
-- Masayuki Nakano <masa...@d-toybox.com> Working on DOM, Events, editor and IME handling for Gecko