scattergl does not display points in Firefox

[antoinerg]

I don't have a reproducible example of this but a user showed me a scattergl trace with lots of datapoints not displaying markers in Firefox (although Chrome was fine). This was inside a Dash app running dash-core v0.43.0 so plotly.js' version was v.1.44.1. Although the points were invisible, the hoverlabels were properly rendered.

Maybe related to #3413

@plotly/plotly_js

[etpinard]

Let's merge this in #3413, until we have a reproducible example.