On a website with active directory membership and role provider active, the tab for Find is missing. 

The Find tab relies on SearchAdmins group as well as WebEditors. Those groups cannot be created in Active directory and adding virtual roles for WebEditors and SearchAdmins does not work.

In the <episerver.framwork> section of Web.config file try changing from:

<virtualRoles addClaims="true">

to:

<virtualRoles addClaims="false" replacePrincipal="true">

Adding DOMAIN from the mappedRole does the trick.

<add name="SearchAdmins" type="EPiServer.Security.MappedRole, EPiServer.Framework" roles="WebAdmins, Administrators,

DOMAIN\Intra Admin" mode="Any"/>