Nastavíš mu dock in parent container:


Např.:

 this.webBrowser1 = new System.Windows.Forms.WebBrowser();
            this.SuspendLayout();
            // 
            // webBrowser1
            // 
            this.webBrowser1.Dock = System.Windows.Forms.DockStyle.Fill;
            this.webBrowser1.Location = new System.Drawing.Point(0, 0);
            this.webBrowser1.MinimumSize = new System.Drawing.Size(20, 20);
            this.webBrowser1.Name = "webBrowser1";
            this.webBrowser1.Size = new System.Drawing.Size(284, 264);
            this.webBrowser1.TabIndex = 0;