Inconsistent behavior with numeric/non-numeric z values in heatmap

Hi,
I have a problem with a plotly heatmap in a shiny app, it is ok in Chrome but wrong in Firefox (Windows 10). And it happens until you click the heatmap. Here is the built app where I got the problem: https://violetr.shinyapps.io/tidytuesdaytweets/. Any idea?

Code to generate an app with only the heatmap:

library(shiny)
library(plotly)
#> Loading required package: ggplot2
#> 
#> Attaching package: 'plotly'
#> The following object is masked from 'package:ggplot2':
#> 
#>     last_plot
#> The following object is masked from 'package:stats':
#> 
#>     filter
#> The following object is masked from 'package:graphics':
#> 
#>     layout
library(tidyverse)
library(lubridate)
#> 
#> Attaching package: 'lubridate'
#> The following object is masked from 'package:base':
#> 
#>     date

# Define UI for application that draws a histogram
ui <- shinyUI(fluidPage(

  # Application title
  title = "example_firefox",
  h2("The graph:"),
  plotlyOutput("distPlot", height = "160px", width = "550px"),
  hr()
))


server <- shinyServer(function(input, output) {
  all_dates_period <-
    tibble(gen_date = as_date(as_date("2018-04-01"):as_date("2018-12-22"))) %>%
    mutate(
      month_name = month(gen_date, TRUE),
      week_num = epiweek(gen_date), # to  start on Sun
      week_day = wday(gen_date, TRUE),
      n = 0
    )

  base_to_heatmap <- all_dates_period %>%
    select(-month_name, -gen_date)

  output$distPlot <- renderPlotly({
    to_heatmap <-
      base_to_heatmap %>%
      spread(key = week_num, value = n) %>%
      as.data.frame()

    matrix_heatmap <- as.matrix(to_heatmap)
    matrix_heatmap <- matrix_heatmap[ nrow(matrix_heatmap):1, ]

    mycols <- c("#ebedf0", "#c6e48b", "#7bc96f", "#239a3b", "#196127")
    mypalette <- colorRamp(mycols)
    library(plotly)
    plot_ly(
      z = matrix_heatmap,
      type = "heatmap",
      colors = mypalette, xgap = 0.5, ygap = 0.5,
      showscale = FALSE
    ) %>%
      layout(
        yaxis = list(
          ticks = "",
          # ticktext = lab_row_days,
          tickmode = "array",
          tickfont = list(color = "86888A"),
          tickvals = 0:6,
          zeroline = FALSE
        ),
        xaxis = list(
          side = "top",
          # ticktext = lab_column_months,
          ticks = "",
          tickmode = "array", tickangle = 0,
          tickfont = list(color = "86888A"),
          tickvals = 0:38,
          zeroline = FALSE
        )
      ) %>%
      config(displayModeBar = FALSE)
  })
})

# Run the application
shinyApp(ui = ui, server = server)

Shiny applications not supported in static R Markdown documents

^{Created on 2019-01-08 by the reprex package (v0.2.1)}

Start with the minimal Shiny app in the issue and run its plot_ly heatmap reproduction in Chrome and Firefox. Focus on the matrix_heatmap passed as z and the differing behavior before and after clicking. Done means the supplied heatmap renders consistently without requiring a click.