--- a/toolkit/components/telemetry/pingsender/pingsender_unix_common.cpp
+++ b/toolkit/components/telemetry/pingsender/pingsender_unix_common.cpp
@@ -172,19 +172,19 @@ static size_t DummyWriteCallback(char* p
 // If we can't use curl's URL parsing (which is safer) we have to fallback
 // to this handwritten one (which is only as safe as we are clever.)
 bool FallbackIsValidDestination(const string& aUrl) {
   // Lowercase the url
   string url = aUrl;
   std::transform(url.begin(), url.end(), url.begin(),
                  [](unsigned char c) { return std::tolower(c); });
   // Strip off the scheme in the beginning
-  if (url.find_first_of("http://") != std::string::npos) {
+  if (url.find("http://") == 0) {
     url = url.substr(7);
-  } else if (url.find_first_of("https://") != std::string::npos) {
+  } else if (url.find("https://") == 0) {
     url = url.substr(8);
   }
 
   // Remove any user information. If a @ appeared in the userinformation,
   // it would need to be encoded.
   unsigned long atStart = url.find_first_of("@");
   url = (atStart == std::string::npos) ? url : url.substr(atStart + 1);