Consider adding overscroll to Smoothfox.js

[crying-qwq]

Consider adding an option in Smoothfox.js to enable overscroll (apz.overscroll.enabled)

It only works on touchpads (and presumably touchscreens).

How it looks:

overscroll.mp4

[yokoffing]

apz.overscroll.enabled is already true(enabled by default) on Firefox Stable and Nightly on my Macbook.

What am I missing here?

[crying-qwq]

Oh okay, sorry. It seems like it is not on by default on Linux (at least not on Fedora's build), didn't think to test that on other platforms

[yokoffing]

No, I appreciate the feedback. I don't have a Linux machine to test at this time, and there's not a lot of documentation around scrolling prefs.

I can include it if it's not default for Linux. And apz.overscroll.enabled was included in previous Smoothfox builds, but I think I removed it because I assumed it was default on all platforms.

I've slated this for next release. Please let me know if you have any other suggestions.