Different behaviour of encodeURIComponent() in Firefox only

Question

I encode a filename and send it as a part of URL like /rest/get?name=Filename.txt. In JS link construction is as simple as

url = '/rest/get?name=' + window.encodeURIComponent(file.name);

It works good for simple cases but for hardcore testing I use a file named

你好abcABCæøåÆØÅäöüïëêîâéíáóúýñ½§!#¤%&()=`@£$€{[]}+´¨^~'-_,;.txt

After URI encoding I expect to get a link

/rest/get?name=%E4%BD%A0%E5%A5%BDabcABC%C3%A6%C3%B8%C3%A5%C3%86%C3%98%C3%85%C3%A4%C3%B6%C3%BC%C3%AF%C3%AB%C3%AA%C3%AE%C3%A2%C3%A9%C3%AD%C3%A1%C3%B3%C3%BA%C3%BD%C3%B1%C2%BD%C2%A7%3F%3FabcABC%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD!%23%C2%A4%25%26()%3D%60%40%C2%A3%24%E2%82%AC%7B%5B%5D%7D%2B%C2%B4%C2%A8%5E~%27-_%2C%3B.txt

And I get it. The constructed link works ok in the latest versions of IE and Chrome but fails in Firefox. After some investigation I've found that in Firefox encodeURIcomponent works differently. Here's actual result in Firefox:

/rest/get?name=%3F%3FabcABC%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD%EF%BF%BD!%23%EF%BF%BD%25%26%28%29%3D%60%40%EF%BF%BD%24%3F{[]}%2B%EF%BF%BD%EF%BF%BD^~%27-_%2C%3B.txt

Visual comparison (Chrome link is on the left and Firefox link is on the right):

I've also tried to copy and paste the valid link (constructed in Chrome) to Firefox and it works ok.

Why do I get different results?
I̶s̶ ̶i̶t̶ ̶a̶ ̶b̶u̶g̶ ̶w̶i̶t̶h̶ ̶̶e̶n̶c̶o̶d̶e̶U̶R̶I̶c̶o̶m̶p̶o̶n̶e̶n̶t̶(̶)̶̶ ̶i̶n̶ ̶F̶i̶r̶e̶f̶o̶x̶?̶
Does Firefox use a different encoding in encodeURIComponent()?

UPD. I've found similar questions (encodeURIComponent behaves differently in browsers for China as location [搜索] and encodeURIComponent difference with browsers and ä-ö-å characters [äöå]), both without an answer.

UPD.2 Further investigation has shown that the following characters are encoded differently and causing 'File not found' exception on server:

• 你好
• æøåÆØÅäöüïëêîâéíáóúýñ
• ½§¤
• £€

Answer 1

I suppose your problem is not the encodeURIComponent() method. It's the encoding of whatever constructs file.name. Extend your question. How is file.name initialized? Where do the chars come from?