weird colors with "light" background tiles

[tim-salabim]

When using tile providers with "light" colors (e.g. standard OpenStreetmap) the polygon fill colors get all messed up unless opacity is set to 1.

You can (maybe) reproduce this issue when replacing this line with L.tileLayer('https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png').addTo(map);

In Firefox on linux (Ubuntu 18.04) with default opacity I see:

whereas with opacity set to 1 I see:

Any ideas what might cause this strange behaviour? I am assuming this has something to do with shaders, but I have no experience with glsl.

For completeness, this was reported at r-spatial/leafgl#4 where some more information can be found and which points to a browser issue as for some combinations of OS and browser this seems to be not a problem.

[nheir]

It look like its related to the premultipliedAlpha parameters of WebGL context canvas

https://bugzilla.mozilla.org/show_bug.cgi?id=1391190