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Can't decompress recovered jsonlz4 session file

  • 3 replies
  • 1 has this problem
  • Last reply by cor-el

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I recovered a deleted 'previous.jsonlz4' file from my SSD but FF (56.0.2) seems to ignore it completely and also tools like the "Session History Scrounger" or command line decompression tools like dejsonlz4.v1.1 or lz4_v1_8_1_win64 cannot decompress it. The file however seems to have the right size and that it has been recovered successfully. It is pretty big BTW with like 2,5 MB.

Is there a way to analyze the recovered file and to tell why it cannot be compressed?

I am using FF 56.0.2 with the TabGroup Add-on

All Replies (3)

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hi, you could try - despite its title it should also work for sessionrestore files.

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Thanks Philipp! There I get the following error: "failed JSON parsing: SyntaxError: JSON.parse: unexpected end of data at line 1 column 1 of the JSON data" and the text area stays blank. Kind regards

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If you recover (undelete) a file then it isn't guaranteed that the file isn't corrupted. Especially with bigger files and possibly fragmentation chances get lower and some clusters may have been reused.

You can use this code in the Browser Console to decompress a LZ4 file.

var {classes:Cc,interfaces:Ci,utils:Cu} = Components;
function decompressFile(oFilePath,nFilePath){
  return Task.spawn(function* () {
    var jsonString = yield,{compression:"lz4"});
    yield OS.File.writeAtomic(nFilePath, jsonString);})
// Set up file chooser
var fp = Cc[";1"].createInstance(Ci.nsIFilePicker);
var fu = Cu.import("resource://gre/modules/FileUtils.jsm").FileUtils
fp.init(window, "Open File", Ci.nsIFilePicker.modeOpen);
fp.appendFilter("Bookmarks/Session (.jsonlz4)","*.jsonlz4");
fp.appendFilter("Search Engines (.mozlz4)","*.mozlz4");
fp.appendFilter("Add-ons Files (.lz4)","*.lz4");
fp.displayDirectory = fu.File(OS.Path.join(OS.Constants.Path.profileDir, "sessionstore-backups"));
// Call file chooser => {
  if (aResult == Ci.nsIFilePicker.returnOK) {
  if (fp.file.exists() && fp.file.isFile() && fp.file.isReadable()) {
    var oldfile = fp.file.path;
    var newfile = oldfile + ".json";
    try {
      decompressFile(oldfile, newfile);
      console.log("Saved as: \"" + newfile + "\"");
      if(confirm("Open JSON file in a Firefox tab?")){
        var uri="file:///"+newfile.replace(/\\/g, "/");, "_blank");
    catch (err) {console.log(err);}
  } else {console.log("<error>");}
  } else {console.log("<canceled>");}