Nothing special... see below which hosts 5 browsers on tabs; note that
WebBrowser might not truly load if it isn't Visible. Check that your
browser is actually *inside* the tab page, and not behind it. The
"Document Outline" window can make this easier to see.

Marc

using System;
using System.Windows.Forms;

static class Program {
   [STAThread]
   static void Main() {
       Application.EnableVisualStyles();
       using (Form f = new Form())
       using (TabControl tc = new TabControl()) {
           for (int i = 0; i < 5; i++) {
               TabPage page = new TabPage("Page " + i.ToString());
               tc.TabPages.Add(page);
               WebBrowser wb = new WebBrowser();
               wb.Name = "WB" + i.ToString();
               f.Load += delegate {
                   wb.Navigate(@"http://www.google.com");
               };
               wb.DocumentCompleted += delegate {
                   f.Text += ";" + wb.Name;
               };
               wb.Dock = DockStyle.Fill;
               page.Controls.Add(wb);
           }
           tc.Dock = DockStyle.Fill;
           f.Controls.Add(tc);
           Application.Run(f);
       }
   }
}