FF freeze resolved with v.2.5.3 Rated 5 out of 5 stars
I had mentioned Firefox freezing when opening the extension preferences of DH v.2.5.2, the problem is resolved with late v.2.5.3, great!
In fact, on my configuration, it wasn't the fact of opening the extension preferences, but opening it when "MediaWeight" enabled was unchecked (from previous version 2.5) or when unchecking it (after previous version 2.5 had been removed, including its data in prefs.js).
All now is well, and 'Video Download Helper' remains my everyday FF Video Downloader. Brilliant!