browser(firefox): fixes empty string postData override (#11529)

Relates #11470
Blocks #11421

browser_patches/firefox-beta/BUILD_NUMBER

@@ -1,2 +1,2 @@
-1314
-Changed: lushnikov@chromium.org Sat Jan  8 18:49:01 MSK 2022
+1315
+Changed: ross.wollman@gmail.com Wed Jan 19 09:15:42 PST 2022

browser_patches/firefox-beta/juggler/NetworkObserver.js

@@ -250,7 +250,7 @@ class NetworkRequest {
     }
     if (method)
       this.httpChannel.requestMethod = method;
-    if (postData)
+    if (postData !== undefined)
       setPostData(this.httpChannel, postData, headers);
   }
 

browser_patches/firefox/BUILD_NUMBER

@@ -1,2 +1,2 @@
-1314
-Changed: lushnikov@chromium.org Tue 18 Jan 2022 02:42:08 AM PST
+1315
+Changed: ross.wollman@gmail.com Tue Jan 18 21:20:13 PST 2022

browser_patches/firefox/juggler/NetworkObserver.js

@@ -250,7 +250,7 @@ class NetworkRequest {
     }
     if (method)
       this.httpChannel.requestMethod = method;
-    if (postData)
+    if (postData !== undefined)
       setPostData(this.httpChannel, postData, headers);
   }