Code:
<xf:breadcrumb source="$forum.getBreadcrumbs()" />
Replace with:
Code:
<xf:breadcrumb source="$forum.getBreadcrumbs()" />
<xf:pageaction if="$forum.canCreateThread()">
<xf:button href="{{ link('forums/post-thread', $forum) }}" class="button--cta" icon="write">
{{ phrase('post_thread') }}
</xf:button>
</xf:pageaction>