Try javascript: URL

I managed to get what I want with this (pretty nasty indeed) workaround: a javascript: URL that creates and immediately submits the form. This means, when you define your search engine, instead of a URL like this:

http://www.example.com/search?term=%s

you would use this URL/code:

javascript:document.write('<form name="f" action="http://www.example.com/search" method="POST"><input type="hidden" name="term" value="%s"></form><script>f.submit();</script>');

Since it'll most likely be a pretty long string it's better to prepare it in a text editor and then copy-paste it into the URL bar.

Example: This is the search URL for an Italian-English dictionary:

javascript:document.write('<form name="f" action="http://dizionari.repubblica.it/cgi-bin/inglese/find" method="POST"><input type="hidden" name="lemma" value="%s"><input type="hidden" name="sez" value="ita"></form><script>f.submit();</script>');

And here the same thing again, but with the single line manually reformatted into multiple lines to make it easier to read and understand:

document.write(
    '
        <form
            name="f"
            action="http://dizionari.repubblica.it/cgi-bin/inglese/find"
            method="POST"
        >
            <input
                type="hidden" 
                name="lemma" 
                value="%s"
            >
            <input
                type="hidden"
                name="sez"
                value="ita"
            >
        </form>
        <script>
            f.submit();
        </script>
    '
);

P.S. Unfortunately, this method doesn't work when performing search from empty "New Tab" page. This can be fixed by installing "Ultimate New tab" extension.

You can use some alternative to speedbit for your downloads like Free Download Manager or Orbit Downloader. However you can try to uninstall the speedbit and then give a try to install it through customize options.

After selecting the Custom Installation option you can choose either to make it default downloader or not.

Now uncheck the checked box I think this is what which is installing the search engine on PC. Also see how to set custom search engine in Google Chrome.