Firefox is now trying to conform to the latest keypress event spec, that is, keypress event should be dispatched only when a key press produces a character input (e.g., typing 'KeyA', 'Space', etc) and Enter key press (Enter, Shift+Enter and Control+Enter for compatibility both with backward and the other browsers). I.e., 'Tab', Shift + 'Space', Ctrl + 'A' etc won't cause keypress event even on Firefox too. You can test this with setting "dom.keyboardevent.keypress.dispatch_non_printable_keys_only_system_group_in_content" in about:config to true on Firefox 60 or later (60 is currently Beta). If you use Firefox Nightly, you also need to ensure that your Etherpad URI is not included in "dom.keyboardevent.keypress.hack.dispatch_non_printable_keys".

Then, you can test this with the following steps:

0. Download Firefox Nightly or Firefox Beta, install it and launch it. https://www.mozilla.org/en-US/firefox/channel/desktop/
1. Open an Etherpad.
2. Type someting.
3. Type 'Tab' key.

Then, the paragraph should be indented. However, nothing happens.

We will include major public Etherpad URLs into the blacklist. So, be careful at testing.

Bug at Mozilla: https://bugzilla.mozilla.org/show_bug.cgi?id=1455059