(function () {
    // Firefox only TTFI
    // need pref to be activated
    // If the "event" has happend, it will return 0
    const timing = window.performance.timing;
    if (timing.timeToFirstInteractive && timing.timeToFirstInteractive > 0) {
        return Number(
            (timing.timeToFirstInteractive - timing.navigationStart).toFixed(0)
        );
    } else return undefined;
})();

@@ -6,16 +6,13 @@
 tion
- 
 () %7B%0A
-  
   //
@@ -30,18 +30,16 @@
 ly TTFI%0A
-  
   // nee
@@ -61,18 +61,16 @@
 tivated%0A
-  
   // If 
@@ -111,18 +111,16 @@
 eturn 0%0A
-  
   const 
@@ -157,18 +157,16 @@
 ming;%0A  
- 
- 
 if (timi
@@ -239,18 +239,20 @@
     
-    return
+const ttfi =
  Num
@@ -256,22 +256,16 @@
 Number(%0A
-      
       (t
@@ -338,17 +338,136 @@
     
+);%0A
     
-);%0A  
+// We have seen cases when TTFI is - 46 years.%0A    if (ttfi %3C 0) %7B%0A      return 0;%0A    %7D else %7B%0A      return ttfi;%0A    %7D%0A
   %7D 

Fix so we don't report negative values #879 (#880)