After a long search, I finally found a solution.
Maybe someone will have the same problem and will need a solution.
For reminder: I can't use the import feature for uploading a JSON file!
The window keeps closing when I try to select a file!
This is supposedly known bug in Google Chrome that appears in Ubuntu and some Windows builds.
Solution: A good workaround is to open the extension url, chrome-extension://nkbihfbeogaeaoehlefnkodbefgpgknn/popup.html, directly in a new tab and import through the tab.
maybe someone will use it