Given following log snippets, their explanation, and nothing else, explain what failure, if any, occurred during build of this package.

  Snippets are in a format of [X] : [Y], where [X] is a log snippet, and [Y] is the explanation.

  Snippets are delimited with '================'.

  Drawing on information from all snippets, provide a concise explanation of the issue and recommend a solution.

  Explanation of the issue, and recommended solution, should take a handful of sentences.

  Snippets:

  [curl: (22) The requested URL returned error: 404
]: [Download of the external script has failed with HTTP return code 404 (can't be reached).]
=============
[error: Executing url helper "/usr/bin/curl --proto -all,+https,+ftps  --silent --show-error --fail --globoff --location -o /var/lib/copr-rpmbuild/results/run-mozilla.sh https://hg.mozilla.org/mozilla-central/raw-file/tip/build/unix/run-mozilla.sh" failed with status 22
error: Couldn't download https://hg.mozilla.org/mozilla-central/raw-file/tip/build/unix/run-mozilla.sh]: [During the SRPM creation the helper script (https://hg.mozilla.org/mozilla-central/raw-file/tip/build/unix/run-mozilla.sh) used to create the RPM couldn't be downloaded by curl so execution of the script has failed.]

Issue: A script used to create RPM during the SRPM creation step can't be downloaded because it is  not reachable on the given URL.

Because SRPM can't be created the RPM build can't be executed.
Resolution: Please make sure that the script is available on the given link. If not please fix the link.

Another possibility is that the build environment doesn't have internet access or doesn't have access to this specific URL. In that case you should enable access of this URL in the build environment.