Use Shift + Esc to open Firefox's Task Manager, find the frozen tab, and click "End Process" to close it without affecting other tabs.

Using Firefox's built-in Task Manager would be safest. However, if Firefox is frozen, you can go to the "Details" tab in the Windows Task Manager and look for that Process ID. But if it's the main process, and not just a specific website or tab process, it would kill Firefox to End Task on that process, so hopefully you won't have to go there.

If Firefox is hung waiting for the network, perhaps disconnecting from the network would wake it up?

I cant got in any of the firefox, it was not responding so I cant open the task manager on firefox I mean firefox's data is stll stored, so it's not lost if I can unfreeze the not responding firefox

In the Windows 10 Task Manager, Details tab:

(1) Click that "Image" or "Name" column heading to sort all the firefox.exe processes together. Can you spot process 7928?

(2) To obtain further information about what process it is, right-click any column heading and choose Select Columns. Then add the Command Line column.

The main Firefox process usually has no extra parameters after firefox.exe in the command line. Don't kill that one except if you need to crash Firefox (losing private tabs).

The processes for individual tabs usually have -isForBrowser in the command line (see attached image). I think killing one of those if needed will not bring down the browser.