In Browser.html home page, this element.setVisible() raises an error below:

JavaScript error: http://localhost:6060/components/Main.js, line 10: InvalidNodeTypeError: The supplied node is incorrect or has an incorrect ancestor for this operation.

It calls this visibility() with the page iframe as the element.
But at the very first time, the iframe looks newly created and out of DOM tree;
And it turns out to fail element.setVisible() and raise the exception.

So fixed to check element is surely under document before element.setVisible().
Otherwise, skip it.

With this fix, each element's first call of visibility() is ignored.
But such brand-new element should be visible and it does not make any problem, I think.

Check environment is below:

• OS: Ubuntu 16.04.3 LTS
• Browser: Graphene
  • Patched to enable mozbrowser for http://
    • KSR-Yasuda/graphene-gecko@aa984ab
  • And set user_pref("dom.mozBrowserFramesEnabledForContent", true); in user.js in profile.

(Recreated the previous request stuck in Travis CI check.)