[Affected versions]
Release 77.0 (64-bit)
Beta 78.0b5 (64-bit) (64-bit)
Firefox Nightly 79.0a1 (2020-06-10) (32-bit)

[Affected platforms]
( macOS 10.14 (Mojave))

[Steps to reproduce]

1- Launch the Firefox Browser and open two https://docs.google.com/spreadsheets and two https://www.office.com/launch/Excel
2- Create a table in both editors and have some cells with date format.
3- Select table from google docs and copy
4- Paste it in the other google docs spreadsheet.
5- Notice that the cell content for the date, is transformed into a number format.
6- Now select table from onedrive and copy.
7- Paste it in the other onedrive spreadhsheet.
8- Content matches perfectly.

[Expected result]
the table's format should match

[Actual result]
Format changes.

Note this is different from https://bugzilla.mozilla.org/show_bug.cgi?id=1641019, since it's not from one editor to a different editor, but within the same editor

With Google Docs Spreadsheets this works on Ubuntu 18.04 with current Nightly.

Clara: can you please retry this on Mac, also for date cells which aren't in a table? Would also be interesting to know, if this works with Chrome.

Hi Mirko,

It's working both in Chrome and FF (nightly 84.0a1 (2020-10-29) (64-bit), release 82.0.2 and beta 83.0b5 (64-bit), for date cells both in a table or not.

Let me know if I can help with anything else.

Best,
Clara