After installation AJAX enabled layered navigation extension, namely Fast AJAX for Layered Navigation and SEO Layered Navigation Plus, should be manually adjusted to current theme. To be more precise, layout of the product list (grid) should be adjusted.

Category Page

1. Open manapro_filterajax.xml

At first, please copy app/design/frontend/base/default/layout/manapro_filterajax.xml to app/design/frontend/[your package]/[your theme]/layout/manapro_filterajax.xml and open it for editing. 

2. Copy product list layout from catalog.xml

Initially, category page is loaded using layout defined in app/design/frontend/[your package]/[your theme]/layout/catalog.xml. The layout of product list block can be found inside <layout>...<catalog_category_layered>...<reference name="content"> tag and looks like the following:

<block type="catalog/category_view" name="category.products" template="catalog/category/view.phtml">

  <block type="catalog/product_list" name="product_list" template="catalog/product/list.phtml">

    <block type="catalog/product_list_toolbar" name="product_list_toolbar" template="catalog/product/list/toolbar.phtml">

      <block type="page/html_pager" name="product_list_toolbar_pager"/>

    </block>

    <action method="addColumnCountLayoutDepend"><layout>empty</layout><count>6</count></action>

    <action method="addColumnCountLayoutDepend"><layout>one_column</layout><count>5</count></action>

    <action method="addColumnCountLayoutDepend"><layout>two_columns_left</layout><count>4</count></action>

    <action method="addColumnCountLayoutDepend"><layout>two_columns_right</layout><count>4</count></action>

    <action method="addColumnCountLayoutDepend"><layout>three_columns</layout><count>3</count></action>

    <action method="setToolbarBlockName"><name>product_list_toolbar</name></action>

  </block>

</block>

The layout instructions above are from standard Magento themes. Your theme can introduce slight modification to it (like adding breadcrumbs block, setting fixed number of columns, etc. 

Copy these instructions from your catalog.xml file to clipboard, we will need it in a minute.

3. Paste into manapro_filterajax.xml and save.

After first filter is applied on the page it is refreshed via AJAX. Actually, all the page stays the same, only category products and layered navigation itself are updated using layout instructions from manapro_filterajax.xml, inside <layout>..<manapro_filterajax_category_view>. The instructions look like the ones below:

<block type="catalog/category_view" name="category.products" template="catalog/category/view.phtml">

  <block type="catalog/product_list" name="product_list" template="catalog/product/list.phtml">

    <block type="catalog/product_list_toolbar" name="product_list_toolbar" template="catalog/product/list/toolbar.phtml">

      <block type="page/html_pager" name="product_list_toolbar_pager"/>

    </block>

    <action method="addColumnCountLayoutDepend"><layout>empty</layout><count>6</count></action>

    <action method="addColumnCountLayoutDepend"><layout>one_column</layout><count>5</count></action>

    <action method="addColumnCountLayoutDepend"><layout>two_columns_left</layout><count>4</count></action>

    <action method="addColumnCountLayoutDepend"><layout>two_columns_right</layout><count>4</count></action>

    <action method="addColumnCountLayoutDepend"><layout>three_columns</layout><count>3</count></action>

    <action method="setToolbarBlockName"><name>product_list_toolbar</name></action>

  </block>

</block>

So, remove these instructions and instead of them paste what you have in clipboard - instructions from catalog.xml. 

That's all needed to do. Save, upload and test.

Search Results Page

The same 3 steps apply to search results page, only locations differ. You need to copy layout block <block type="catalogsearch/result" ..>.. </block> from catalogsearch.xml <layout>..<catalogsearch_result_index>..<reference name="content"> and paste it into manapro_filterajax.xml, into <layout>...<manapro_filterajax_search_index>, instead of the same, but differently laid out <block type="catalogsearch/result"..>..</block>.