[test/fix] prevent FirefoxHelper from silently failing to start This was breaking some tests without any obvious error message and you should fail as early as possible to make debugging easier. Closes #17260390

version=3
opts=uversionmangle=s/(rc|a|b|c)/~$1/ \
https://pypi.debian.net/cubicweb/cubicweb-(.+)\.(?:zip|tgz|tbz|txz|(?:tar\.(?:gz|bz2|xz)))