(In reply to itd from comment #7)
I think the release note is misleading. There are a lot of Notes Webmails on premise and they have still this bug.
The preference that applies old behavior to specific hosts can be edited manually to list additional hosts. Do we need a support article on that? Roughly speaking, here are the steps:
(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.
(2) In the search box above the list, type or paste hack and pause while the list is filtered
What do you have listed for the value of the dom.keyboardevent.keypress.hack.use_legacy_keycode_and_charcode preference? Firefox 66.0.2 should update it to the following (all on one line), although I needed to restart Firefox an extra time to reflect it:
You can add a new host name to the beginning or end of the list: beginning followed by comma and no space, or end, following a comma with no space.