Clicking links in pdfs opened with Okular opens Abiword (instead of the default browser)

The answer by @Marius is correct. It helped me. Just a clarification.

1. Run kcmshell4 filetypes in a console or by Alt+F2. File Associations - KDE Control Module will open.
2. Search for html and select the file type text/html.
3. Move the application name you want to be a default for html in the "Application Preference Order" to the top.

For newer KDE versions you might need to run:

kcmshell4 componentchooser

and set the "Web Browser" to the command of your preferred browser.

This worked on Arch Linux, at least.

The answer can be found in the okular devel list here

The important part is quoted here

Is it linking to an html file? If so you might want to also check which is the default application in kcmshell4 filetypes for html mimetype.