Reeborg: two major steps forward, a huge step back with Firefox

UPDATE: The Firefox problem was caused by using a function argument named "watch" ... which seemed like a good name...  However, it appears to conflict with https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/watch

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I'm really happy with two new cool features for Reeborg's World ... but this happiness is nearly crushed by the fact that Reeborg's World is completely broken by Firefox 42.0.  It still works with Google Chrome and even works with Microsoft Edge (gasp!) ... but not with Firefox.  I tried to load a year old version of the site that did work with older version of Firefox: no go.

The two new features: it is possible to enable a "variable watch".

Of course, the speed of the animation can be controlled and even paused.

It is also possible to control Reeborg (or, write any Python code, really) using an REPL.