--- a/testing/geckodriver/CHANGES.md
+++ b/testing/geckodriver/CHANGES.md
@@ -1,15 +1,16 @@
 # Change log
 
 All notable changes to this program is documented in this file.
 
 ## Unreleased
 
 ### Added
+- Added preference `dom.file.createInChild` set to true to allow file object creation in content processes.
 - New window `state` field on the window rect response object, returned from [`GetWindowRect`], [`SetWindowRect`], [`MinimizeWindow`], [`MaximizeWindow`], and [`FullscreenWindow`] commands
 
 [`FullscreenWindow`]: https://docs.rs/webdriver/0.29.0/webdriver/command/enum.WebDriverCommand.html#variant.FullscreenWindow
 [`GetWindowRect`]: https://docs.rs/webdriver/0.29.0/webdriver/command/enum.WebDriverCommand.html#variant.GetWindowRect
 [`MaximizeWindow`]: https://docs.rs/webdriver/0.29.0/webdriver/command/enum.WebDriverCommand.html#variant.MaximizeWindow
 [`MinimizeWindow`]: https://docs.rs/webdriver/0.29.0/webdriver/command/enum.WebDriverCommand.html#variant.MinimizeWindow
 [`SetWindowRect`]: https://docs.rs/webdriver/0.29.0/webdriver/command/enum.WebDriverCommand.html#variant.SetWindowRect
 

--- a/testing/geckodriver/src/prefs.rs
+++ b/testing/geckodriver/src/prefs.rs
@@ -1,12 +1,12 @@
 use mozprofile::preferences::Pref;
 
 lazy_static! {
-    pub static ref DEFAULT: [(&'static str, Pref); 79] = [
+    pub static ref DEFAULT: [(&'static str, Pref); 80] = [
         // Disable automatic downloading of new releases
         ("app.update.auto", Pref::new(false)),
 
         // Disable automatically upgrading Firefox
         ("app.update.enabled", Pref::new(false)),
 
         // Increase the APZ content response timeout in tests to 1
         // minute.  This is to accommodate the fact that test environments
@@ -119,16 +119,19 @@ lazy_static! {
         ("datareporting.healthreport.uploadEnabled", Pref::new(false)),
         ("datareporting.policy.dataSubmissionEnabled", Pref::new(false)),
         ("datareporting.policy.dataSubmissionPolicyAccepted", Pref::new(false)),
         ("datareporting.policy.dataSubmissionPolicyBypassNotification", Pref::new(true)),
 
         // Disable popup-blocker
         ("dom.disable_open_during_load", Pref::new(false)),
 
+        // Enabling the support for File object creation in the content process
+        ("dom.file.createInChild", Pref::new(true)),
+
         // Disable the ProcessHangMonitor
         ("dom.ipc.reportProcessHangs", Pref::new(false)),
 
         // Disable slow script dialogues
         ("dom.max_chrome_script_run_time", Pref::new(0)),
         ("dom.max_script_run_time", Pref::new(0)),
 
         // Only load extensions from the application and user profile

--- a/testing/marionette/server.js
+++ b/testing/marionette/server.js
@@ -177,16 +177,19 @@ const RECOMMENDED_PREFS = new Map([
   ["datareporting.healthreport.uploadEnabled", false],
   ["datareporting.policy.dataSubmissionEnabled", false],
   ["datareporting.policy.dataSubmissionPolicyAccepted", false],
   ["datareporting.policy.dataSubmissionPolicyBypassNotification", true],
 
   // Disable popup-blocker
   ["dom.disable_open_during_load", false],
 
+  // Enabling the support for File object creation in the content process
+  ["dom.file.createInChild", true],
+
   // Disable the ProcessHangMonitor
   ["dom.ipc.reportProcessHangs", false],
 
   // Disable slow script dialogues
   ["dom.max_chrome_script_run_time", 0],
   ["dom.max_script_run_time", 0],
 
   // Only load extensions from the application and user profile