On my personal devices Mathjax looks like
Whereas on other devices Mathjax looks like
For example, the arrow between $R^4$ and $R^4$ is thicker in the first picture and thin in the second.
The edges of the letter “T” are shorter in the first one and longer in the second one.
The letter “R” in $R^4$ looks different in both pictures.
Why does Mathjax do this?