[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
Document: cubicweb-doc
Title: CubicWeb Documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developers
Section: Programming
Format: HTML
Index: /usr/share/doc/python3-cubicweb-documentation/html/index.html
Files: /usr/share/doc/python3-cubicweb-documentation/html/*