Re-write / edit a URL to remove a prefix ad

[Chris_P_Cook]

How do I edit a URL to remove a prefix advert
e.g.

http://adsite.com/a/b/c.htm/http://real ... /x/y/z.htm
re-writes and opens
http://realsite.com/x/y/z.htm

The filters I have tried just block the ad site

Thanks
Chris

[Wladimir Palant]

That's what Redirect Remover is good for: https://addons.mozilla.org/addon/537