How to check if a website is open in a web browser?

You will need to write an API to manipulate tabs in browsers other than Internet Explorer, but you can start Internet Explorer processes and list open windows / tabs like this:

using SHDocVw;
....
    public class IEClass
    {
        List<InternetExplorer> IEWindows;

        public IEClass()
        {
            IEWindows = new List<InternetExplorer>();
        }

        public List<InternetExplorer> GetIEInstances()
        {
            IEWindows.Clear();
            ShellWindows shellWindows = new ShellWindows();
            string filename;

            foreach (InternetExplorer ie in shellWindows)
            {
                filename = Path.GetFileNameWithoutExtension(ie.FullName).ToLower();
                if (filename.Equals("iexplore"))
                {
                    IEWindows.Add(ie);
                }
            }
            return IEWindows;
        }

        public bool QuitInstance(int key)
        {
            InternetExplorer ie = (InternetExplorer)IEWindows[key];

            try
            {
                ie.Quit();
                return true;
            }
            catch (Exception ex)
            {
                // handle any exception
            }
            return false;
        }

        public void StartInstance(string url)
        {
            InternetExplorer ie = new InternetExplorer();

            ieInstance.Visible = true;
            ieInstance.Navigate2(ref (object)url, ref Empty, ref Empty, ref Empty, ref Empty);
            IEWindows.Add(ie);
        }
    }

      

        
        
        
      

    

This is not the most efficient code, but it works for getting existing instances, creating new instances, and excluding Internet Explorer windows / tab instances. I tested it on Windows XP IE 6 through Windows 7 IE 10.

I also wrote some C ++ to get the foreground window information that you could use to read the window title and process name to determine if any tab is open:

HWND foregroundWindow = GetForegroundWindow();
DWORD* processID = new DWORD;
GetWindowText(foregroundWindow, buf, 255);
GetWindowThreadProcessId(foregroundWindow, processID);
DWORD p = *processID;
HANDLE hProcess = OpenProcess(PROCESS_QUERY_INFORMATION |
                              PROCESS_VM_READ,
                              FALSE, p);
TCHAR szProcessName[MAX_PATH];

if (NULL != hProcess )
{
    HMODULE hMod;
    DWORD cbNeeded;

    if ( EnumProcessModules( hProcess, &hMod, sizeof(hMod),
                             &cbNeeded) )
    {
        GetModuleBaseName( hProcess, hMod, szProcessName,
                           sizeof(szProcessName)/sizeof(TCHAR) );
    }
}
CloseHandle(hProcess);

      

        
        
        
      

    

You can wrap this code in a C ++ DLL or call Windows API functions from pinvoke in C #.

This is the rough equivalent of C ++ code in C #:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;

namespace ForegroundWindowTest
{
    class Program
    {
        [DllImport("user32.dll")]
        private static extern IntPtr GetForegroundWindow();

        [DllImport("user32.dll")]
        static extern int GetWindowTextLength(IntPtr hWnd);

        //  int GetWindowText(
        //      __in   HWND hWnd,
        //      __out  LPTSTR lpString,
        //      __in   int nMaxCount
        //  );
        [DllImport("user32.dll")]
        private static extern int GetWindowText(IntPtr hWnd, StringBuilder lpString, int nMaxCount);

        //  DWORD GetWindowThreadProcessId(
        //      __in   HWND hWnd,
        //      __out  LPDWORD lpdwProcessId
        //  );
        [DllImport("user32.dll")]
        private static extern uint GetWindowThreadProcessId(IntPtr hWnd, out uint lpdwProcessId);

        //HANDLE WINAPI OpenProcess(
        //  __in  DWORD dwDesiredAccess,
        //  __in  BOOL bInheritHandle,
        //  __in  DWORD dwProcessId
        //);
        [DllImport("kernel32.dll")]
        private static extern IntPtr OpenProcess(uint dwDesiredAccess, bool bInheritHandle, uint dwProcessId);

        [DllImport("kernel32.dll")]
        private static extern bool CloseHandle(IntPtr handle);

        //  DWORD WINAPI GetModuleBaseName(
        //      __in      HANDLE hProcess,
        //      __in_opt  HMODULE hModule,
        //      __out     LPTSTR lpBaseName,
        //      __in      DWORD nSize
        //  );
        [DllImport("psapi.dll")]
        private static extern uint GetModuleBaseName(IntPtr hWnd, IntPtr hModule, StringBuilder lpFileName, int nSize);

        //  DWORD WINAPI GetModuleFileNameEx(
        //      __in      HANDLE hProcess,
        //      __in_opt  HMODULE hModule,
        //      __out     LPTSTR lpFilename,
        //      __in      DWORD nSize
        //  );
        [DllImport("psapi.dll")]
        private static extern uint GetModuleFileNameEx(IntPtr hWnd, IntPtr hModule, StringBuilder lpFileName, int nSize);

        public static string GetTopWindowText()
        {
            IntPtr hWnd = GetForegroundWindow();
            int length = GetWindowTextLength(hWnd);
            StringBuilder text = new StringBuilder(length + 1);
            GetWindowText(hWnd, text, text.Capacity);
            return text.ToString();
        }

        public static string GetTopWindowName()
        {
            IntPtr hWnd = GetForegroundWindow();
            uint lpdwProcessId;
            GetWindowThreadProcessId(hWnd, out lpdwProcessId);

            IntPtr hProcess = OpenProcess(0x0410, false, lpdwProcessId);

            StringBuilder text = new StringBuilder(1000);
            //GetModuleBaseName(hProcess, IntPtr.Zero, text, text.Capacity);
            GetModuleFileNameEx(hProcess, IntPtr.Zero, text, text.Capacity);

            CloseHandle(hProcess);

            return text.ToString();
        }


        static void Main(string[] args)
        {
            while (!Console.KeyAvailable)
            {
                Console.WriteLine(GetTopWindowText());
                Console.WriteLine(GetTopWindowName());
            }
        }
    }
}

      

        
        
        
      

    

You can also check this answer here: How to get URLs of open pages from Chrome and Firefox?