Este é um bug do Opera Mini.
this search.js will start poping up if you close a tab which is the page not finished to load, there is another reason why this problem occurs, if you open and loads many link in just a single time, some of the link will stop loads and this 'search.js' will pop up.
There is not an exact solution but we can do advanced things, so that this problem will be minimized. If you want to open many links, make sure that to open and to finish load it one by one. You can also restart your Operamini after 30-minutes to 1-hour of using. Minimize also on Opening some website having a big size before it finished loading, these website examples are site that don't have a mobile version.
Eu tentaria usar um navegador diferente, se possível.