Each time I open Firefox, I get this error. I have NoScript installed. There also isn't any tabs open that has anything to do with this website. I tried clearing my cache and local content, but it still keeps coming.
NoScript detected a potential Cross-Site Scripting attack from [...] to https://smartfonts.com. Suspicious data: (URL) https://smartfonts.com/{{metaImage}}
I had the same, after visiting a wikipedia page. To get rid of it click the plus sign to open a new tab. Firefox will then show some recent visited page previews, use the elipsis (3 dots) menu to remove the relevant entry from the firefox history.