I have been testing Beta Version 1.5.4b2 on two systems running, severally, Ubuntu® 16.04.1-LTS (LinUX Kernel Family 4.4.0-49-generic as of 21 November 2016) and Microsoft® Windows® 10 Build 1607 10.0.14393.447. All systems go for both so far. On previous versions I found the "restore forward button" feature to work properly on both rigs, and this would be of use for those needing a stable but compact complete URLbar on any OS Mozilla supports. All other functions this Extension work as advertised.
Update, 24 November 2016: In Beta Version 1.5.4b3, both "Navigation Toolbar Buttons: OSX" in Classic Style For... and "Restore hidden forward button" in Other Tweaks up and working as advertised.