Warns you if a link is to a pdf, exe, mailto, or anything not that isn't a web page. It does this by placing an icon after the link. See the picture for more details. You can personalize it to your own needs by adding or removing your own file types.

This style uses icons from Windows. Linux users, check out Link Warning Mod (Linux compatible). Mac users, do you guys even use Firefox? This system isn't foolproof because it merely checks the end of the url. Also, this style works in Gecko only.

Inspired by PDF-icon after links to PDFs, PDF file warning with custom hover cursor, PDF / mailto Icon, and target="_blank".

Supported types: .pdf, .doc, .xls, .ppt, .7z, .zip, .rar, .exe, .msi, .mov, .m3u, .pls, .asx, mp3, .avi., .wma, .wmv, .mpg, .wav, mailto:

Update 1: added .torrent, .nzb, aim:, irc:, _blank, _new, and iTunes Music Store
Update 2: added .asf, news:, nntp:
Update 3: added .xpi; cleaned up code
Update 4: added .docx, .xlsx, .pptx