According to the docs, this doesn't fire on just any random website's links, only in specific parts of the Firefox UI:
To improve the loading speed, Firefox will open predictive connections to sites when the user hovers their mouse over thumbnails on the New Tab Page or the user starts to search in the Search Bar, or in the search field on the Home or the New Tab Page. In case the user follows through with the action, the page can begin loading faster since some of the work was already started in advance.
That's fortunate, because firing it on any website's hover link would reach that nightmare scenario pretty quickly.
Link prefetcing on websites only happens if the site explicitly marks the link for prefetch. (Example use case: prefetch page 2 of an article from page 1.) Firefox & Chrome have done this for years.