We fixed the main issue of this form in CVE-2020-9444, but the audit
done at that time only included links found in rendered_markdown; this
change completes our audit for links with target=_blank anywhere in
the codebase.
Previously, in narrow viewports, the "filter"
option would disappear, which was very confusing.
This commit moves the filter streams input to the
next line, making it visible at all viewport widths.
@showell modified the commit message and got Casper
tests passing.
Fixes#12898.