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.
Many Thanks for your support throughout.
First thing this morning, I opened the page that first displayed the symptoms. The page worked. Bug gone. No changes at all. But that made me even more curious and just more than a bit scared.
So I opened Windows 7, FF, and jsfiddle, and then ran that code and the bug was once more visible. Hang on Linux, “Gah. Your tab just crashed.” on Win 7 Latest Firefox ESR.
Jsfiddle url is : JsFiddle showing faulty code it is literally the above code cut and pasted. All are x86_64 arch, all Firefoxes are ESR’s.
I will investigate a bit more and let you know. Perhaps it is an interaction with builtin pdf-viewer/youtube/plugin or something I will let you know if I discover root cause. Many Thanks.