Clipboard URL Normalizer — Jefik

Firefox's browser.urlbar.decodeURLsOnCopy setting forces a choice: keep spaces as %20 but also percent-encode non-ASCII characters like kanji and accented letters, or decode everything and get literal spaces in copied URLs. There's no built-in middle ground.
This extension fills that gap. It monitors the clipboard in the background and normalizes any copied URL, regardless of your Firefox setting:

If the URL has percent-encoded sequences (%XX), it decodes them first — preserving structural characters like %2F, %23, and %3F
Then re-encodes any spaces as %20

The result is always a clean URL with readable non-ASCII characters and properly encoded spaces.