I have following:
- Latest Mega Filter pro
- Current themePavilion v2.1.1
- BurnEngine version1.1.1
- OpenCart version1.5.6.4
- vQmod version2.6.1
- HTTP ServerApache/2
- MySQL server version10.1.22-MariaDB
- PHP version7.0.17

I followed these instructions:
http://support.themeburn.com/topic/mega-filter-pro-by-attribs-options-brands-price-filters

The filter works, as in updating the page after marking a choice in the filter front end, until I enter .tb_widget_products_system into the “Content selector (in JavaScript):” field.

When doing step 3 in the tutorial, it breaks the javascript.
Then I get these errors in the console (and the page does not update after doing a choice in the filter module):

Uncaught TypeError: Cannot read property ‘top’ of undefined
at http://mydomain.com/catalog/view/javascript/mf/mega_filter.js?v1.3.1.1:2248:54
at MegaFilter._showLoader (http://mydomain.com/catalog/view/javascript/mf/mega_filter.js?v1.3.1.1:2256:6)
at MegaFilter.ajax (http://mydomain.com/catalog/view/javascript/mf/mega_filter.js?v1.3.1.1:2441:8)
at MegaFilter.runAjax (http://mydomain.com/catalog/view/javascript/mf/mega_filter.js?v1.3.1.1:1993:10)
at HTMLDivElement.stop (http://mydomain.com/catalog/view/javascript/mf/mega_filter.js?v1.3.1.1:2100:11)
at t.(anonymous function).(anonymous function)._trigger (http://mydomain.com/image/cache/tb/main_73f210fcd683e2c9ad5df2f5cf7a9f97.script.js?176402099:40:10036)
at t.(anonymous function).(anonymous function)._stop (http://mydomain.com/image/cache/tb/main_73f210fcd683e2c9ad5df2f5cf7a9f97.script.js?176402099:41:31149)
at t.(anonymous function).(anonymous function)._stop (http://mydomain.com/image/cache/tb/main_73f210fcd683e2c9ad5df2f5cf7a9f97.script.js?176402099:40:5029)
at t.(anonymous function).(anonymous function)._mouseStop (http://mydomain.com/image/cache/tb/main_73f210fcd683e2c9ad5df2f5cf7a9f97.script.js?176402099:41:29639)
at t.(anonymous function).(anonymous function)._mouseStop (http://mydomain.com/image/cache/tb/main_73f210fcd683e2c9ad5df2f5cf7a9f97.script.js?176402099:40:5029)

I have turned OFF cache in BurnEngine, and for the sake of it also cleared the cache.

If I revert back to use the #mfilter-content-container selector, the filter works well.

The only thing that does not wotk well is that the grid view of the products loose all CSS.