Update Mozilla Firefox icon

[foo-dogsquared]

Issue: #1824

Checklist

• I updated the JSON data in _data/simple-icons.json
• I optimized the icon with SVGO or SVGOMG
• The SVG viewbox is 0 0 24 24

Description

There is an official monochrome version offered from the asset pack in their logo usage guide.
The SVG from the asset pack is pretty optimized and only needs scaling to fit the Simple Icons specs.

As for the color update, I chose it from their color design guide.

The chosen color is based from the pictured hues from the official palette.

Initially, I have chosen four colors: the middle two variants of each hue.

Here are the hex values for easy referencing: #FFBD4F, #FFA537, #FE8A4F, and #FF7139.
As you can see from the pull request, I ended up with #FF7139 since I feel it is the closest color to the updated colors to the original.

[ericcornelissen]

Thanks for the quick update 👌 I agree with your choice of colour (it being close to the old colour seems like a good measure to me) but because of its ambiguity I will leave it to one of the other @simple-icons/maintainers to merge.