my css has the following rule:
p + p {text-indent:6mm}

a second footnote on the same page inherits this indentation. How can I prevent this?

Perhaps I should add that I have tried the following:
.inline-fn {
float: footnote;
footnote-style-position:inside;
font-size: .85em;
line-height: 1.27em;
}
.inline-fn + .inline-fn {
text-indent: 0;
margin-top:3pt;
color:red;
}
But .inline-fn + .inline-fn does not work, probably because they are not next to each other in the source document.

How about this:

p + p:not(.inline-fn) { ... }

Thanks Mike, I had found out in the meanwhile that I should simply do .inline-fn {text-indent:0}. I had not completely understood the mechanism. For some reason my reply to the forum got lost though (probably forgot to press Post...).