Everything is working ok here in Firefox. What version are you running? Do you have any extensions enabled? Particularly ad, content or script blockers? Can you reproduce the issue while all extensions are disabled?
Unfortunately as we've had no further reports of this, it is likely something exclusive to your specific browser install. You may want to consider uninstalling/reinstalling the browser or using a different browser entirely. Another solution which may work for your own site is using a different CDN source for your jQuery files. It seems you're currently using the Google one. You could try the jQuery CDN ore even just serve it locally.
The recommendation by otto may also be reasonable.
Failing all this, logging a support request with Mozilla directly may help.