Steps to Reproduce

1. run the code

<spreadsheet id="ss" vflex="1" width="100%"  showToolbar="true"/>

2. visit with firefox 84.0.2
3. click "New Book"
4. enter "test" at A1
5. press Ctrl+c
6. reload the page, click "New Book"
7. press ctrl+v at A1

Current Result

it pastes 3 cells, test is at A3

Expected Result

test is at A1

Debug Information

1. when pressing ctrl+v, there is a wrong event fired

cmd_0	"onClipboardPaste"
uuid_0	"r6GM0"
data_0	"{\"sheetId\":\"lc_sheet_0\",\"left\":0,\"top\":0,\"right\":0,\"bottom\":2,\"values\":[[\"\"],[\"\"],[\"test\"]]}"

2. chrome doesn't have this bug and will show test at A1
3. if you don't reload the page, the bug doesn't happen.