Current slide not opaque.

[sgparry]

The following presentation has slides separated in Z. When viewing it, the current slide transparency never reaches 100% - You can still see slides that are notionally "behind it".

{
"slides": [
{
"components": [],
"z": -3000,
"impScale": 3,
"rotateX": 0,
"rotateY": 0,
"rotateZ": 0,
"index": 0,
"selected": false,
"active": false,
"markdown": "# 1!\n",
"x": 600,
"y": 170
},
{
"components": [],
"z": -6000,
"impScale": 3,
"rotateX": 0,
"rotateY": 0,
"rotateZ": 0,
"index": 1,
"selected": true,
"active": true,
"markdown": "# 0!\n",
"x": 904,
"y": 172,
"background": "bg-solid-orange"
},
{
"components": [],
"z": -10000,
"impScale": 9,
"rotateX": 0,
"rotateY": 0,
"rotateZ": 0,
"index": 2,
"selected": false,
"active": false,
"background": "bg-solid-yellow",
"x": 768,
"y": 369
},
{
"components": [],
"z": -500,
"impScale": 3,
"rotateX": 0,
"rotateY": 1.4,
"rotateZ": 0,
"index": 3,
"selected": false,
"active": false,
"background": "bg-transparent",
"x": 1256,
"y": 193
}
],
"background": "bg-solid-purple",
"activeSlide": {
"components": [],
"z": -6000,
"impScale": 3,
"rotateX": 0,
"rotateY": 0,
"rotateZ": 0,
"index": 1,
"selected": true,
"active": true,
"markdown": "# 0!\n",
"x": 904,
"y": 172,
"background": "bg-solid-orange"
},
"__genid": 405,
"fileName": "3D Test 3",
"deckVersion": "1.0",
"customBackgrounds": {
"bgs": []
},
"overviewX": 928,
"overviewY": 269.5
}

[sgparry]

OK, I've found the cause: It's a bug in Firefox:
https://bugzilla.mozilla.org/show_bug.cgi?id=725299
basically FF ignores the 3d stacking when any element is not opaque.
Partial workaround: if we amend the CSS for .step and .step.active so that .step.active z-index is greater than .step z-index, at least the current slide will be correctly visible.
Thoughts?