When I'm logged in and I try to add a new portlet I usually click:
"Add" -> "More" and simply select my portlet.

The problem is that when the popup with the list of available portlets shows up the existing portlets get moved to the right, which is unacceptable in my theme.

I think it's a matter of some JavaScript script that handles the popup. How do I disable moving the portlets then?

Hi,
The shifting of portlets are just normal as the "add" dropdown takes some space.

Hi Dan,
You can use below CSS class in your theme :

.lfr-has-sidebar #main-content {
padding-left: 0px;
}

@Jignesh Vachhani

Thanks a lot ;-) No more moving/shifting ;-)

Btw. it's in the dockbar.css file ;-)

You can also set below CSS using Manage pages section:

1) Go to Manage Pages >> CSS section
And put below CSS in CSS box which have been provided at bottom:
.lfr-has-sidebar #main-content {
padding-left: 0 !important;
}