--- a/devtools/bootstrap.js
+++ b/devtools/bootstrap.js
@@ -91,17 +91,17 @@ function interpretPreprocessingInstructi
 // Read a preference file and set all of its defined pref as default values
 // (This replicates the behavior of preferences files from mozilla-central)
 function processPrefFile(url) {
   let content = readURI(url);
   content = interpretPreprocessingInstructions(content);
   content.match(/pref\("[^"]+",\s*.+\s*\)/g).forEach(item => {
     let m = item.match(/pref\("([^"]+)",\s*(.+)\s*\)/);
     let name = m[1];
-    let val = m[2];
+    let val = m[2].trim();
 
     // Prevent overriding prefs that have been changed by the user
     if (Services.prefs.prefHasUserValue(name)) {
       return;
     }
     let defaultBranch = Services.prefs.getDefaultBranch("");
     if ((val.startsWith("\"") && val.endsWith("\"")) ||
         (val.startsWith("'") && val.endsWith("'"))) {