Issue 5285 - Fix saving filters on clean Thunderbird or SeaMonkey profiles

lib/io.js

Index: lib/io.js
===================================================================
--- a/lib/io.js
+++ b/lib/io.js
@@ -71,32 +71,43 @@ function callLegacy(method, ...args)
 
 function legacyFile(fileName)
 {
   let file = LegacyIO.resolveFilePath("adblockplus");
   file.append(fileName);
   return file;
 }
 
+function ensureDirExists(file)
+{
+  if (!file.exists())
+  {
+    ensureDirExists(file.parent);
+    file.create(Ci.nsIFile.DIRECTORY_TYPE, 0o755);
+  }
+}
+
 let fallback = {
   readFromFile(fileName, listener)
   {
     let wrapper = {
       process(line)
       {
         if (line !== null)
           listener(line);
       }
     };
     return callLegacy("readFromFile", legacyFile(fileName), wrapper);
   },
 
   writeToFile(fileName, data)
   {
-    return callLegacy("writeToFile", legacyFile(fileName), data);
+    let file = legacyFile(fileName);
+    ensureDirExists(file.parent);

[Wladimir Palant, 2017/06/01 09:16:41]

For reference, this operation was originally being performed by filterStorage.
Obviously, it no longer makes sense to have it there.

+    return callLegacy("writeToFile", file, data);
   },
 
   copyFile(fromFile, toFile)
   {
     return callLegacy("copyFile", legacyFile(fromFile), legacyFile(toFile));
   },
 
   renameFile(fromFile, newName)