Here is what I'm using, the user agent can be successfully set, while download preferences cannot.
Windows 7, Chrome 26, Selenium-dotnet-2.31.2, chromedriver_win_26.0.1383.0
ChromeOptions chromeOptions = new ChromeOptions();
var prefs = new Dictionary<string, object> {
{ "download.default_directory", @"C:\code" },
{ "download.prompt_for_download", false }
};
chromeOptions.AddAdditionalCapability("chrome.prefs", prefs);
chromeOptions.AddArgument("--user-agent=" + "some safari agent");
var driver = new ChromeDriver(chromeOptions);
Taken from chromedriver.log:
[1.201][FINE]: Initializing session with capabilities {
"browserName": "chrome",
"chrome.prefs": {
"download.default_directory": "C:\\code",
"download.prompt_for_download": false
},
"chrome.switches": [ "--user-agent=Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/534.57.2 (KHTML, like Gecko) Version..." ],
"chromeOptions": {
"args": [ "--user-agent=Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/534.57.2 (KHTML, like Gecko) Version..." ],
"binary": "",
"extensions": [ ]
},
"javascriptEnabled": true,
"platform": "WINDOWS",
"version": ""
}
Check the temp Preferences file at *temp\Google\Chrome\User Data\Default\Preferences, no "default_directory" and "prompt_for_download" are set.
"download": {
"directory_upgrade": true
},