Firefox Browser Console - Save Current Session

FirefoxSaveSession.js

/* Session Backup Script for the Browser Console

   NOTE: BEFORE RUNNING THIS SCRIPT, CHECK THIS SETTING:
   Type or paste about:config into the address bar and press Enter
   Click the button promising to be careful
   In the search box type devt and pause while Firefox filters the list
   If devtools.chrome.enabled is false, double-click it to toggle to true

Paste this entire script into the command line at the bottom of the Browser Console (Windows: Ctrl+Shift+j)
Then press Enter to run the script. A save dialog should promptly open.
*/
ssj = SessionStore.getBrowserState(); // get Current Session State
if(ssj){
	// Set up Save As dialog
	var fp = Components.classes["@mozilla.org/filepicker;1"].createInstance(Components.interfaces.nsIFilePicker);
	try { // Fx125+
		fp.init(window.browsingContext, 'Open File', Components.interfaces.nsIFilePicker.modeSave);
	} catch(e) { // Fx124 and earlier
		fp.init(window, 'Open File', Components.interfaces.nsIFilePicker.modeSave);
	}
	fp.appendFilter("JSON Files", "*.json");
	fp.defaultString = "sessionstore-snapshot.json";
	// Call Save As dialog
	fp.open((aResult) => {
		if (aResult == Components.interfaces.nsIFilePicker.returnOK ||
			aResult == Components.interfaces.nsIFilePicker.returnReplace) {
			try {
				IOUtils.writeUTF8(fp.file.path, ssj);
				alert('Look for ' + fp.file.path);
			} catch (err) {
				alert(err);
			}
		} else {
			alert('Okay, not saving');
		}
	});
}

Had to update from OS.File.writeAtomic() to IOUtils.writeUTF8() for Firefox 104.

Could not write session state file out of memory undefined
and us this:
Uncaught out of memory

Sorry for the delay in picking up your comment. I can't think of a solution for "out of memory".

The problem has been solved. I mistakenly used 32-bit Firefox. (It's really an unexpected mistake)

No one told me that the error was caused by the memory limit of the 32-bit program. A while ago, I was stuck in Firefox crash without knowing why......

Try/catch added for Firefox 125 (currently in Nightly), at lines 16-18, 20.