Vega-lite difference between Firefox and Chrome - vega

Question

I have a vega-lite chart that shows up as expected in Chrome (72.0.3626.96), but not in Firefox (70.0.1). I have checked the spec in the Vega Editor. Does anyone know why this might be?
Here are the rendered charts:
Firefox:
Chrome:
Here is the spec:
Any help you might be able to give would be much appreciated.
Apologies, but I do not know how to collapse this code.
{
"$schema": "https://vega.github.io/schema/vega-lite/v3.2.1.json",
"background": "white",
"config": {"mark": {"tooltip": null}, "view": {"height": 300, "width": 400}},
"datasets": {
"data-511198e25d4dbee99248144390684caa": [
{
"counts": 338,
"filter_method": "greater than",
"grade": "9",
"index": 3,
"perc": 0.2669826224328594,
"school_code": "Board",
"threshold": "8",
"year": 20172018,
"year_lab": "2017/18",
"year_lab_q": "2017"
},
{
"counts": 414,
"filter_method": "greater than",
"grade": "9",
"index": 4,
"perc": 0.30689399555226093,
"school_code": "Board",
"threshold": "8",
"year": 20182019,
"year_lab": "2018/19",
"year_lab_q": "2018"
}
],
"data-72a083843a98847e44077116c495e448": [
{
"counts": 49,
"filter_method": "greater than",
"grade": "9",
"index": 0,
"perc": 0.3356164383561644,
"school_code": "KING",
"threshold": "8",
"year": 20142015,
"year_lab": "2014/15",
"year_lab_q": "2014"
},
{
"counts": 62,
"filter_method": "greater than",
"grade": "9",
"index": 5,
"perc": 0.3668639053254438,
"school_code": "MLTS",
"threshold": "8",
"year": 20162017,
"year_lab": "2016/17",
"year_lab_q": "2016"
},
{
"counts": 53,
"filter_method": "greater than",
"grade": "9",
"index": 6,
"perc": 0.29608938547486036,
"school_code": "KING",
"threshold": "8",
"year": 20172018,
"year_lab": "2017/18",
"year_lab_q": "2017"
},
{
"counts": 44,
"filter_method": "greater than",
"grade": "9",
"index": 7,
"perc": 0.25882352941176473,
"school_code": "MLTS",
"threshold": "8",
"year": 20172018,
"year_lab": "2017/18",
"year_lab_q": "2017"
},
{
"counts": 53,
"filter_method": "greater than",
"grade": "9",
"index": 8,
"perc": 0.3212121212121212,
"school_code": "KING",
"threshold": "8",
"year": 20182019,
"year_lab": "2018/19",
"year_lab_q": "2018"
},
{
"counts": 61,
"filter_method": "greater than",
"grade": "9",
"index": 9,
"perc": 0.25206611570247933,
"school_code": "MLTS",
"threshold": "8",
"year": 20182019,
"year_lab": "2018/19",
"year_lab_q": "2018"
}
]
},
"height": 400,
"layer": [
{
"data": {"name": "data-72a083843a98847e44077116c495e448"},
"encoding": {
"color": {
"field": "school_code",
"legend": {"labelFontSize": 15, "titleFontSize": 20},
"title": null,
"type": "nominal"
},
"tooltip": [
{
"field": "perc",
"format": ".2%",
"title": "percentage",
"type": "quantitative"
},
{
"field": "counts",
"title": "number",
"type": "quantitative"
},
{"field": "year_lab", "title": "school year", "type": "nominal"},
{"field": "school_code", "title": "level", "type": "nominal"},
{"field": "grade", "type": "nominal"},
{"field": "filter_method", "type": "nominal"},
{"field": "threshold", "type": "nominal"}
],
"x": {
"axis": {"format": "%Y", "tickCount": 5},
"field": "year_lab_q",
"scale": {"domain": ["2013.9", "2018.5"]},
"title": "School Year (beginning)",
"type": "temporal"
},
"y": {
"axis": {"format": ".0%"},
"field": "perc",
"title": "Percentage",
"type": "quantitative"
}
},
"mark": {"point": true, "type": "line"},
"selection": {
"selector001": {
"bind": "scales",
"encodings": ["x", "y"],
"type": "interval"
}
}
},
{
"data": {"name": "data-511198e25d4dbee99248144390684caa"},
"encoding": {
"color": {
"field": "school_code",
"legend": {"labelFontSize": 15, "titleFontSize": 20},
"scale": {"domain": ["Board"], "range": ["black"]},
"title": null,
"type": "nominal"
},
"tooltip": [
{
"field": "perc",
"format": ".2%",
"title": "percentage",
"type": "quantitative"
},
{
"field": "counts",
"title": "number",
"type": "quantitative"
},
{"field": "year_lab", "title": "school year", "type": "nominal"},
{"field": "school_code", "title": "level", "type": "nominal"},
{"field": "grade", "type": "nominal"},
{"field": "filter_method", "type": "nominal"},
{"field": "threshold", "type": "nominal"}
],
"x": {"field": "year_lab_q", "type": "temporal"},
"y": {"field": "perc", "type": "quantitative"}
},
"mark": {"point": true, "type": "line"}
}
],
"resolve": {"scale": {"color": "independent"}},
"title": "A title!",
"width": 700
}

Answer 1

It appears that your temporal values are not being parsed correctly in firefox (details of javascript date parsing behavior is often browser-dependent). You could try forcing the correct parsing by changing your data specification (in both places) to:
"data": {
"name": "data-72a083843a98847e44077116c495e448",
"format": {"parse": {"year_lab_q": "date:%Y"}}
}
This should ensure that the year string is parsed as a year, rather than e.g. a unix timestamp.
The other place date parsing is happening is in your domain specification. You might try changing those to a more standard time format, e.g.
"domain": ["2013-11-01", "2018-06-01"]