FF: Mirador in second tab is empty after loading

[radpet]

mirado2.zip

Loading mirador in iframe inside display:none parent causes the image to be loaded but not shown.

Steps to reproduce
Open test.html
Wait until the image is loaded.
Go to tab 2
See that there is no image shown, although it loads the image and if you go to the element which displays the image and set its style to display:block it will show it.

It happens under Firefox only. Maybe it is because mirador does not handle the event that sets its canvas to be visible.

[beaudet]

This is causing an issue with embedding Mirador in ConservationSpace.

[rsinghal]

I can recreate this, but don't know why it's happening. I look forward hearing about any more information you find.

[radpet]

It seems that firefox does not like this line
https://github.com/IIIF/mirador/blob/release2.1/js/src/widgets/imageView.js#L343
Adding display:block !important via class or changing show() to css('display','block') also works.
I'll be working on this and send pr as soon as I find better way to fix it. By the way it might be jquery show() issue on firefox but I am not sure yet. Any other ideas?