Fix intermittent disappearing imagery on Firefox

[pastcompute]

mapbox-gl-js version: v0.20.1 running in Firefox 47.0.1 on Windows 7 x64

Steps to Trigger Behavior

Code:

1. Instantiate a map using satellite imagery
2. Add a couple of layers and data sources inside map.on() method

Execution:

1. Browse to the demo, hit run
2. After the map renders, F5 then Run
3. Repeat until bug occurs.

Expected Behavior

Should see data points over satellite imagery

Actual Behavior

Intermittently, after the satellite imagery is loaded and visible, the background will go white and you will only see the data points

Demo:

https://cdn.rawgit.com/pastcompute/html5-demos/master/mapbox-intermittent-no-imagery.html

Notes

I am experiencing this in a much more complex application, map.on is wrapped in a promise to simulate the environment of my application. Although I don't think the promise is the problem.

In my case, often it will happen on the first render after F5, whereas the demo it sometimes takes quite a few attempts to cause the problem to occur.

Doesn't seem to happen in Chrome .

Firefox also seems flickery compared to chrome, which sees a smooth transition of the imagery.

[lucaswoj]

potentially related to #1680 #1679

[pastcompute]

Just an update, this still happens with mapbox-gl-js 0.22.0 and Firefox upgraded to 48.0
Although it took about 20 retries to repeat the fault using my demo app, the actual app that it occurs in is much more consistent, probably 9 times out of 10. So I'm wondering if it is memory use related somehow

[jfirebaugh]

Closing due to inactivity and age; if this is still an issue in 0.42.2, please open a new issue.