Go to the Font's stylesheet.css and add font-display: block; in all @font-face { }
This Stackoverflow Answer helped me..
Below is the Summary of the answer
If you can access to css of this extension, simply add font-display:block; on font-face definition or send feedback to developer of this extension:)
@font-face {
font-family: ExampleFont;
src: url(/path/to/fonts/examplefont.woff) format('woff'),
url(/path/to/fonts/examplefont.eot) format('eot');
font-weight: 400;
font-style: normal;
font-display: block;
}