How to find default web browser using C#?

You can look here for an example, but mainly it can be done like this:

internal string GetSystemDefaultBrowser()
{
    string name = string.Empty;
    RegistryKey regKey = null;

    try
    {
        //set the registry key we want to open
        regKey = Registry.ClassesRoot.OpenSubKey("HTTP\\shell\\open\\command", false);

        //get rid of the enclosing quotes
        name = regKey.GetValue(null).ToString().ToLower().Replace("" + (char)34, "");

        //check to see if the value ends with .exe (this way we can remove any command line arguments)
        if (!name.EndsWith("exe"))
            //get rid of all command line arguments (anything after the .exe must go)
            name = name.Substring(0, name.LastIndexOf(".exe") + 4);

    }
    catch (Exception ex)
    {
        name = string.Format("ERROR: An exception of type: {0} occurred in method: {1} in the following module: {2}", ex.GetType(), ex.TargetSite, this.GetType());
    }
    finally
    {
        //check and see if the key is still open, if so
        //then close it
        if (regKey != null)
            regKey.Close();
    }
    //return the value
    return name;

}

The other answer does not work for me when internet explorer is set as the default browser. On my Windows 7 PC the HKEY_CLASSES_ROOT\http\shell\open\command is not updated for IE. The reason behind this might be changes introduced starting from Windows Vista in how default programs are handled.

You can find the default chosen browser in the registry key, Software\Microsoft\Windows\Shell\Associations\UrlAssociations\http\UserChoice, with value Progid. (thanks goes to Broken Pixels)

const string userChoice = @"Software\Microsoft\Windows\Shell\Associations\UrlAssociations\http\UserChoice";
string progId;
BrowserApplication browser;
using ( RegistryKey userChoiceKey = Registry.CurrentUser.OpenSubKey( userChoice ) )
{
    if ( userChoiceKey == null )
    {
        browser = BrowserApplication.Unknown;
        break;
    }
    object progIdValue = userChoiceKey.GetValue( "Progid" );
    if ( progIdValue == null )
    {
        browser = BrowserApplication.Unknown;
        break;
    }
    progId = progIdValue.ToString();
    switch ( progId )
    {
        case "IE.HTTP":
            browser = BrowserApplication.InternetExplorer;
            break;
        case "FirefoxURL":
            browser = BrowserApplication.Firefox;
            break;
        case "ChromeHTML":
            browser = BrowserApplication.Chrome;
            break;
        case "OperaStable":
            browser = BrowserApplication.Opera;
            break;
        case "SafariHTML":
            browser = BrowserApplication.Safari;
            break;
        case "AppXq0fevzme2pys62n3e0fbqa7peapykr8v":
            browser = BrowserApplication.Edge;
            break;
        default:
            browser = BrowserApplication.Unknown;
            break;
    }
}

In case you also need the path to the executable of the browser you can access it as follows, using the Progid to retrieve it from ClassesRoot.

const string exeSuffix = ".exe";
string path = progId + @"\shell\open\command";
FileInfo browserPath;
using ( RegistryKey pathKey = Registry.ClassesRoot.OpenSubKey( path ) )
{
    if ( pathKey == null )
    {
        return;
    }

    // Trim parameters.
    try
    {
        path = pathKey.GetValue( null ).ToString().ToLower().Replace( "\"", "" );
        if ( !path.EndsWith( exeSuffix ) )
        {
            path = path.Substring( 0, path.LastIndexOf( exeSuffix, StringComparison.Ordinal ) + exeSuffix.Length );
            browserPath = new FileInfo( path );
        }
    }
    catch
    {
        // Assume the registry value is set incorrectly, or some funky browser is used which currently is unknown.
    }
}

I just made a function for this:

    public void launchBrowser(string url)
    {
        string browserName = "iexplore.exe";
        using (RegistryKey userChoiceKey = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows\Shell\Associations\UrlAssociations\http\UserChoice"))
        {
            if (userChoiceKey != null)
            {
                object progIdValue = userChoiceKey.GetValue("Progid");
                if (progIdValue != null)
                {
                    if(progIdValue.ToString().ToLower().Contains("chrome"))
                        browserName = "chrome.exe";
                    else if(progIdValue.ToString().ToLower().Contains("firefox"))
                        browserName = "firefox.exe";
                    else if (progIdValue.ToString().ToLower().Contains("safari"))
                        browserName = "safari.exe";
                    else if (progIdValue.ToString().ToLower().Contains("opera"))
                        browserName = "opera.exe";
                }
            }
        }

        Process.Start(new ProcessStartInfo(browserName, url));
    }