\operatorname{} doesn't produce <mo>&ApplyFunction;</mo> resulting in different spacing in Firefox

[hbghlyj]

Is your feature request related to a problem? Please describe. $$\sin\left(x\right)$$ and $$\operatorname{sin}\left(x\right)$$ render the same in MathJax CHTML or SVG output but the output MathML render differently in Firefox: Below is MathML produced by the first:

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mi>sin</mi>
  <mo data-mjx-texclass="NONE">&#x2061;</mo>
  <mrow data-mjx-texclass="INNER">
    <mo data-mjx-texclass="OPEN">(</mo>
    <mi>x</mi>
    <mo data-mjx-texclass="CLOSE">)</mo>
  </mrow>
</math>

MathML produced by the second doesn't have <mo data-mjx-texclass="NONE">&#x2061;</mo> :

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mi>sin</mi>
  <mrow data-mjx-texclass="INNER">
    <mo data-mjx-texclass="OPEN">(</mo>
    <mi>x</mi>
    <mo data-mjx-texclass="CLOSE">)</mo>
  </mrow>
</math>

Describe the solution you'd like I would like \operatorname to produce <mo data-mjx-texclass="NONE">&#x2061;</mo> after function name.

Describe alternatives you've considered Adding $\def\operatorname#1{\mathop{\rm #1}}$ solves the problem.

Additional context MathJax v3

[dpvc]

Thanks for the report. I will look into adding the U+2061 after \operatorname