None.
I don’t think it’s a good idea to take some huge collection of prefs and just apply them blindly.
Instead, make the changes that you actually want to do, so that you actually know what changes you are causing. If you want to put those into your user.js file then feel free, but in my opinion it’s just better to change them in about:config directly - that is, unless you need to apply the exact same set of changes to multiple profiles.
Right, and that’s fine. The one good thing about these “collections” is when they describe what the pref does (I mean, so does official source typically). But that matters only as long as the audience actually reads those descriptions. But then if you just pick the ones you actually care about (which you should totally do) it becomes irrelevant from which “collection” you found about it from.
Same. I’m using betterfox and liking it so far.
The good thing is every configuration is well documented so I’m confident to make the changes myself (like enable back account sync - it’s super useful but I don’t know why it was disabled in the first place).
Please tell me how to use one?
I use Firefox Profilemaker.