You're right, it is a font issue. Changing my font size from 16 to 17 fixed the bugs I noted, although other minus signs (in exponents) then disappeared in the process. It seems that the larger the font size, or the more zoomed you are into your browser, the fewer math display issues there are. So before I was using font size 16, zoom 100%, if you want to try reproducing the issue.

In T269222#6662810, @Aklapper wrote:

Hi @Tedjh20, thanks for taking the time to report this and welcome to Wikimedia Phabricator! Cannot reproduce in Firefox 83.
Which exact browser and browser version do you use?
On https://en.wikipedia.org/wiki/Special:Preferences#mw-prefsection-rendering , what is your setting in the "Math" section?

Could you provide a screenshot of how https://wikimedia.org/api/rest_v1/media/math/render/svg/6a35bbf4a7fbba678f1a96b3f2e1127d900143c7 is rendered?