If you accidentally dismissed the dialog that asks for Closing all tabs in Microsoft’s Edge Windows 10 browser (Close All Tabs) and you want Microsoft Edge to shows again the confirmation dialog when you close the browser that has multiple tabs opened you need to make some setting is the registry because Edge will no longer ask you again.
So for recover dismissed the dialog that asks for Closing all tabs in Microsoft’s Edge Windows 10 browser follow steps bellow or just download How to restore Microsoft Edge “Close All Tabs” confirmation dialog after disabling it file, open arhive and run the reg file with administrator rights !
To do it manualy :
1. Click/Tap Start and in search (cortana ) type regedit.exe
2. Search for the HKEY_CURRENT_USER\Software\Classes\Local Settings\Software\Microsoft\Windows\CurrentVersion\AppContainer\Storage\microsoft.microsoftedge_8wekyb3d8bbwe\MicrosoftEdge\Main
3. Double-click the DWORD value named AskToCloseAllTabs
4. Set the value data in AskToCloseAllTabs to 1
5. Exit the Registry Editor.
6. Restart computer
Good luck !