Wrapped anchor tag around inline-flex container - text not underlined in Firefox

I'm trying to nest an inline-flex container inside an anchor tag (IE11 made me do so). Unfortunately I get different results on FireFox compared to Chrom for example. On Chrom the text remains underlined while FF doesn't bother the draw the line at bottom at all.

Any idea why it works this way?

a{  color: red;}.flex{  display: inline-flex;  /* display: flex; */ -> will show the underline}

<a href="www.google.com"><div class="flex">Text inside wrapper</div></a>