JavaScript syntax check reports error, but there is no syntax error in the code

[A9T9]

Describe the problem and steps to reproduce it:

I tried to upload a new addon, but the syntax check reports an error.

How to recreate:

1. Upload this extension:
   Firefox_Opera.a6.zip

2. You will get this error

JavaScript syntax error
Error: There is a JavaScript syntax error in your code; validation cannot continue on this file.
scripts/background.js line 31 column 13

but line 31 looks ok:
changeIcon = (tabId,url) => {

What happened?

Details:

What did you expect to happen?

No syntax error

Anything else we should know?

Extension home page: ColorFish Color Picker

When tested, the addon works fine in Firefox.

[A9T9]

It seems the error is related to the new javascript syntax(es6)?

We changed
changeIcon = (tabId,url) => {
to
changeIcon(tabId,url) {
and the submission worked fine.

[Rob--W]

Duplicate of #2978