6.8.6 version took some hacks for Basilisk.
I've got the toolbar button working on my Basilisk install matching the one on my Pale Moon install. Took some slight modifications of about-openwith.js, openwith.js, and openwith-fx.xul

It is cool seeing Pale Moon icon in my Basilisk and Basilisk icon in my Pale Moon status bars.
Also convenient for checking how sites render in IE, Edge, FF, Chrome easily.

I prefer the 6.8.6 version on my browsers which will continue to support XUL addons.