I'd like to do it, because of the firefox extended-selection feature (acutally it is a XULrunner feature - which is a firefox engine).
Another solution would be to find out where all the KDE help handbooks are located. Do you happen to know that?
Edit: knowing where they are won't help - since them are in a docbook format - not in html.
You cannot use Firefox as your help browser in KDE.
From the Kubuntu-docs package:
Also the KOffice-doc-html package:
In other words, you will just have to use KHelpCenter, or manually convert the files from docbook format to HTML (which I will not cover here as that is out of the scope of the question).