the inner-inner double quotes are breaking your onclick attribute value. Replace them with single quotes and escape them.
...onclick="window.open('https://seals.resellerratings.com/landing.php?seller=myID','name','height=760,width=780,scrollbars=1'); return false;"...
The same thing happens on your oncontextmenu event, perform the same fix.
...oncontextmenu="alert('Copying Prohibited by Law - ResellerRatings seal is a Trademark of All Enthusiast, Inc.'); return false;" />...
full code:
$('#thirdPartyCheckoutButtons').prepend('<a href="https://www.resellerratings.com" onclick="window.open('https://seals.resellerratings.com/landing.php?seller=myID','name','height=760,width=780,scrollbars=1'); return false;"><img style="border:none;" src="//seals.resellerratings.com/seal.php?seller=myID" oncontextmenu="alert('Copying Prohibited by Law - ResellerRatings seal is a Trademark of All Enthusiast, Inc.'); return false;" /></a><img src="https://www.myurl.com/hdsd834k.png" style="float: left;margin-left: 180px;">');?
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…