[Affected versions]
Release 78.0 (64-bit)
Beta 79.0b5 (64-bit)
Firefox Nightly 80.0a1 (2020-07-08) (64-bit) is working a bit different (explained in bottom note)

[Affected platforms]
All

[Steps to reproduce]

1- Launch FF and open https://docs.google.com/spreadsheets/u/0/ (or any type of document, such as slides or docs as it happens as well) with RDM activated.
2- Edit the file as desired (can input some text for instance)
3- Change device
4- Editor mode has switched so now the pencil icon is displayed on top right corner.
5- Click pencil.

[Expected result]
A popup should show up at the bottom asking the user to use the docs/sheets app

[Actual result]
Nothing happens when clicking the pencil icon.

Note: in firefox nightly, with touch simulation on the pop up is displayed, but nothing happens with touch simulation off.