Disable KDE Launcher - Browser history integration

For KDE 4:
Copy /usr/share/kde4/services/plasma-runner-bookmarks.desktop
→ ~/.kde/share/kde4/services/plasma-runner-bookmarks.desktop

For KDE 5:
Copy /usr/share/kservices5/plasma-runner-bookmarks.desktop
→ ~/.local/share/kservices5/plasma-runner-bookmarks.desktop

Replace a line X-KDE-PluginInfo-EnabledByDefault=false.

Relogin.

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Shorthand for the above:

mkdir -p ~/.local/share/kservices5
sed 's/EnabledByDefault=true/EnabledByDefault=false/' \
    /usr/share/kservices5/plasma-runner-bookmarks.desktop \
    > ~/.local/share/kservices5/plasma-runner-bookmarks.desktop

(Inspired by user2798869's answer.) Another option is to create a file /home/(username)/.kde/share/kde4/services/plasma-runner-bookmarks.desktop with contents

X-KDE-PluginInfo-EnabledByDefault=false

This has the advantage over modifying the file in /usr/share/kde4/ that it will certainly persist software updates, and even OS reinstall if you have a separate home partition.

(I have tested this on openSUSE 13.1, where the file path is /home/(username)/.kde4/share/kde4/services/plasma-runner-bookmarks.desktop, but I guess Ubuntu uses .kde instead of .kde4)

Doesn't look like there's any way to do it in the UI.

But, you can edit the /usr/share/kde4/services/plasma-runner-bookmarks.desktop file.

kdesudo kate /usr/share/kde4/services/plasma-runner-bookmarks.desktop

Find this line:

X-KDE-PluginInfo-EnabledByDefault=true

and change it to:

X-KDE-PluginInfo-EnabledByDefault=false

You'll have to restart plasma for it to take effect:

kquitapp plasma-desktop
plasma-desktop

I'm not sure if this change will persist when KDE is updated, though. My recommendation would be to instead avoid all this trouble by just using the lancelot application launcher (package name is plasma-widget-lancelot). I prefer it to kickoff, and it has a UI that allows you to disable the bookmarks runner for the search bar.