This add-on will stop working when Firefox 57 arrives in November 2017 and Mozilla drops support for XUL / XPCOM / legacy add-ons. It should still work on Firefox 52 ESR until ESR moves to Firefox 60 ESR in 2018 (~Q3).
Waterfox and Basilisk browsers are based on Firefox and will keep legacy add-on support.
There is no "please port it" or "please add support for it" this time, because the entire add-on eco system changes and the technology behind this kind of add-on gets dropped without replacement.
The CRSG-add-on for default Firefox theme enables the combined "Reload-Stop-Go"-buttons old visual appearance (on urlbar) like it was on Firefox 4-8.
This add-on does NOT create new buttons!
Firefox 29+: Where to find the combined "Reload-Stop-Go"-button?
The combined "Reload-Stop-Go"-button is already on urlbars end by default.
Firefox 16-28: Where to find the combined "Reload-Stop-Go"-button?
Rightclick on a toolbar -> customize -> look for "reload" and "stop" buttons. Place them like this on navigation toolbar: [...][urlbar][reload][stop][...]
The button only appears on urlbars right end, when both buttons "reload" and "stop" are placed right after the urlbar like on default non-customized Firefox appearance.
This extension is not compatible with themes and extensions that already style the combined "Reload-Stop-Go"-button.
'Classic Toolbar Buttons' add-on
You may also be interested in the classic toolbar buttons like they were on Firefox 4-7 [small icons] and Firefox 4-12 [big icons].
The CRSG-add-on is part of 'Classic Toolbar Buttons' add-on since v1.0.9.
Add-on Compatibility Reporter
If you have any problems, please contact me via email (provided inside my profile). Wrong bugreports via "Add-on compatibility Reporter" without any comments or description won't be helpful.