System.InvalidOperationException: 'Expected browser binary location, but unable to find binary in default location error using Firefox Selenium in C#

This error message...

System.InvalidOperationException: 'Expected browser binary location, but unable to find binary in default location, no 'moz:firefoxOptions.binary' capability provided, and no binary flag set on the command line (SessionNotCreated)'

...implies that the GeckoDriver was unable to initiate/spawn a new Browsing Context i.e. Firefox Browser session.

Possibly firefox browser is installed at a non-conventional location, hence GeckoDriver is unable to access the firefox binary.

Solution

As a solution pass the absolute location of the firefox.exe binary through the BrowserExecutableLocation argument of FirefoxOptions as follows:

FirefoxOptions options = new FirefoxOptions();
options.BrowserExecutableLocation = ("C:\\Program Files\\Mozilla Firefox\\firefox.exe"); //location where Firefox is installed
WebDriver driver = new FirefoxDriver(options);

You need download Mozilla Firefox

https://www.mozilla.org/en-US/firefox/new/

then install Mozilla Firefox.