SeleniumHQ
diff --git a/‎dotnet/src/webdriver/Firefox/FirefoxOptions.cs‎
Lines changed: 28 additions & 0 deletions b/‎dotnet/src/webdriver/Firefox/FirefoxOptions.cs‎
Lines changed: 28 additions & 0 deletions
@@ -58,6 +58,7 @@ public class FirefoxOptions : DriverOptions
         private const string FirefoxArgumentsCapability = "args";
         private const string FirefoxLogCapability = "log";
         private const string FirefoxPrefsCapability = "prefs";
+        private const string FirefoxEnvCapability = "env";
         private const string FirefoxOptionsCapability = "moz:firefoxOptions";
 
         private string browserBinaryLocation;
@@ -66,6 +67,7 @@ public class FirefoxOptions : DriverOptions
         private List<string> firefoxArguments = new List<string>();
         private Dictionary<string, object> profilePreferences = new Dictionary<string, object>();
         private Dictionary<string, object> additionalFirefoxOptions = new Dictionary<string, object>();
+        private Dictionary<string, object> environmentVariables = new Dictionary<string, object>();
 
         /// <summary>
         /// Initializes a new instance of the <see cref="FirefoxOptions"/> class.
@@ -80,6 +82,7 @@ public FirefoxOptions()
             this.AddKnownCapabilityName(FirefoxOptions.FirefoxBinaryCapability, "BrowserExecutableLocation property");
             this.AddKnownCapabilityName(FirefoxOptions.FirefoxArgumentsCapability, "AddArguments method");
             this.AddKnownCapabilityName(FirefoxOptions.FirefoxPrefsCapability, "SetPreference method");
+            this.AddKnownCapabilityName(FirefoxOptions.FirefoxEnvCapability, "SetEnvironmentVariable method");
             this.AddKnownCapabilityName(FirefoxOptions.FirefoxLogCapability, "LogLevel property");
             this.AddKnownCapabilityName(FirefoxOptions.FirefoxLegacyProfileCapability, "Profile property");
             this.AddKnownCapabilityName(FirefoxOptions.FirefoxLegacyBinaryCapability, "BrowserExecutableLocation property");
@@ -211,6 +214,26 @@ public void SetPreference(string preferenceName, string preferenceValue)
             this.SetPreferenceValue(preferenceName, preferenceValue);
         }
 
+        /// <summary>
+        /// Sets an environment variable to be set in the operating system's environment under which the Firerox browser is launched.
+        /// </summary>
+        /// <param name="variableName">The name of the environment variable.</param>
+        /// <param name="variableValue">The value of the environment variable.</param>
+        public void SetEnvironmentVariable(string variableName, string variableValue)
+        {
+            if (string.IsNullOrEmpty(variableName))
+            {
+                throw new ArgumentException("Environment variable name cannot be null or an empty string");
+            }
+
+            if (variableValue == null)
+            {
+                variableValue = string.Empty;
+            }
+
+            this.environmentVariables[variableName] = variableValue;
+        }
+
         /// <summary>
         /// Provides a means to add additional capabilities not yet added as type safe options
         /// for the Firefox driver.
@@ -336,6 +359,11 @@ private Dictionary<string, object> GenerateFirefoxOptionsDictionary()
                 firefoxOptions[FirefoxPrefsCapability] = this.profilePreferences;
             }
 
+            if (this.environmentVariables.Count > 0)
+            {
+                firefoxOptions[FirefoxEnvCapability] = this.environmentVariables;
+            }
+
             foreach (KeyValuePair<string, object> pair in this.additionalFirefoxOptions)
             {
                 firefoxOptions.Add(pair.Key, pair.Value);