achellios

WordPress bloggers will sometimes copy headlines from a WordPress-generated homepage and paste them into the post-editing window. In Firefox, this has the unfortunate result of converting absolute urls into relative ones. For example, copying a headline from http://khaotica.com converts the permalink for this article:
http://khaotica.com/2009/12/firefox-relative-links-fix-wordpress.html
…to a relative link:
../2009/12/firefox-relative-links-fix-wordpress.html
This creates broken links when the post is viewed on the archive page and RSS feed. The links will also be broken for subscribers who receive posts via email.
Enter the Relative Links Fix. This plugin will replace relative urls with the proper absolute urls every time you save or publish a post. If you use WordPress and can’t shake those copy-paste habits, this is the plugin for you.
As always, donations are appreciated. I promise to spend them exclusively on soda (the creative fuel that powers developers everywhere).

Relative Links Fix

Corrects Firefox behavior in which pasting formatted content in the editor converts absolute URLs to relative URLs.

alastairbrayne

Create custom menu items with links relative to the root url of the current wordpress installation.
Simply add a custom link as normal with the url prefixed by %ROOT%. e.g. to get http://mydomain.com/wp/myCustomPage if your wordpress lives at http://mydomain.com/wp then you just write %ROOT%/myCustomPage for your link url.
<h3>Relative Menu Item</h3>
Create custom menu items with links relative to the wordpress root url.
<h3>Important Notes</h3>
Not tested with multisite installations.

Relative Menu Item Plugin

Create custom menu items with links relative to the root url of the current wordpress installation.

Relative Links Fix vs Relative Menu Item Plugin