Fix php and js errors on Joomla 3.9

1 Understand why the Plugin System - Ajax scroll eternal scrolling of goods does not work
2 Deal with the plugin for Joomshoping the previous and next product it flips through the goods as it is necessary and randomly if you set the toars sorting by id then it works if by forced it does not work flips wrong. JoomShopping Products Navigation plugin
3 Remove all errors and warnings in the console
4 hide under spoiler bottom menu
5 Speed up your site with no plugins
6 Make the header on the tablet more competent
7 The web wizard gives such an error Incorrectly configured display of non-existent files and pages. The site is probably incorrectly configured to return a 404 Not Found HTTP code. This can prevent the site from being indexed.
8 When entering the site, you need to display a modal window with the choice of the city i.e. I went to the site and there it will be immediately pedagogical to select the city