private void saveLocation() {
		Program firstProgram = diffPlugin.getFirstProgram();
		if (firstProgram == null) {
			return;
		}
		NavigationHistoryService historyService =
			diffPlugin.getTool().getService(NavigationHistoryService.class);
		if (historyService != null) {
			historyService.addNewLocation(goToService.getDefaultNavigatable());
		}
	}
Saving the first program's location (the left listing) in the navigation history. The second
program's location (the right listing) isn't saved since the navigation is relative to a
program in the tool's main listing. Also, if the second program's locations were saved in the
history, their program wouldn't be found and would cause errors when restarting the
application with the tool and primary program displayed, but no Diff program.
Ghidra/Features/ProgramDiff/src/main/java/ghidra/app/plugin/core/diff/DiffGoToService.java