This issue was pointed out in bugzilla here, and Firefox seems to improve when the option is changed, but it is not yet the case by default.
(Set browser.urlbar.decodeURLsOnCopy to true in about:config)
URLs are supposed to have the aspect of human-readable information, but for a Non-English user, this characteristic is being degraded.
This is because it seems to be a common behavior among browsers that when you try to copy a URL string displayed in the URL bar of a web browser, the URL-encoded string is copied.
This inconvenience seems to have been left unaddressed for a long time. I think this should be improved in a common way in all browsers.