Ok. Reproduce this bug by using the JSfiddle linked above, on any Firefox earlier than current releas(es).
All the Firefox Extended Release versions (ESR’s) crash on it – even in Safe Mode (with all plugins disabled) – seemingly across all platforms. Early FF versions like 46.0.1 32 bit crash across the board on it in safe mode faithfully the older FF’s modal dialog box outline the exception with line numbers which differ each time (canvas.min.js:10/71/82)…
Jsfiddle will not allow debugging ‘…is a blackbox…’ message; although some meaning may be derived from the jsfiddle stack trace by somebody with experience of the inners – but I can’t export it.
Debian LiveCD Firefox 58.0.2 is OK, and thankfully does not wear the Quantum interface. I guess I am going to have to bite it and dump either firefox or canvasjs – sucks to be me.
Summary : Firefox releases earlier than Late 2017 / Early 2018 do not reliably support canvasjs in all scenarios, most likely to bugs in the javascript implimentation.
Many Thanks for your support throughout.