As stated on the Mozilla Developer Network
Gecko started supporting the SVG image format for cursors with version 2.0 (Firefox 4 / Thunderbird 3.3 / SeaMonkey 2.1). However, it is important to note that the SVG image must have a length-valued height and width on its root SVG node, not percentage-valued. Features like JavaScript, CSS animation, and declarative SMIL within an SVG image are disregarded; animated cursor creation using SVG is not possible.
Therefore, it is necessary to explicitly specify the height and width in your .svg file.
The provided .svg file does not have any dimensions declared, as shown below:
<svg xmlns="http://www.w3.org/2000/svg" id="Capa_1" viewBox="0 0 320.995 320.995" x="0px" y="0px" height="200" xmlns:xml="http://www.w3.org/XML/1998/namespace" xml:space="preserve" viewbox="0 0 320.995 320.995" version="1.1">
If you include the width and height attributes, everything should work properly.
Just remember not to use percentages when declaring the dimensions