Actually you can go further and avoid the use of that CSS code to any page by replacing that line with this code:
@-moz-document domain(dailymotion.com){
img[class*="blur"]{filter: none!important}
}
So now it only applies to the img elements with class that contains "blur" text and it is only in a page in dailymotion second level domain.
Aditionally, for those interested in a blur effect instead, I found what was the problem. Was partially by Dailymotion CSS code (
because of this) and Mozilla by not following its
own MDN (they should change "may include an anchor" by "
must include an anchor").
@-moz-document domain(dailymotion.com){
img[class*="blur"]{filter: url("data:image/svg+xml;utf8,<svg height='0' xmlns='http://www.w3.org/2000/svg'><filter id='blur'><feGaussianBlur stdDeviation='1'/></filter></svg>#blur")!important}
}