As Grease Monkey does not seem to work with Fienix in my machine, I thought I could also try Guerilla Scripting. It can be installed via the 'add-ons' menu, at least with the stand-alone version of Fienix.
But I cannot figure out where the scripts should be copied...? (it has to be done manually). The readme file mentions a "guerillajs/scripts" dir, but I cannot localize it. Where should it be? And if I would like to copy the ViewTube script from GreaseMonkey, where is it located? Any help would be appreciated!-)