How to disable "web search" in the location bar of a webbrowser?

Don't know of a way to do exactly what you are looking to do, but may have a couple of alternative solutions.

First is storing your pwds in something like Keepass. The cool thing about this is that when you grab your password (i.e. double click on it). It removes the your password after short period (I think something like 12 seconds).

The second is to turn off instant search in google preferences (http://www.google.com/preferences) -

Edit - Revised Pic (That pic wasn't even close to the right spot...it has been that kind of day...)

Hope this helps!

In Firefox (tested in version 50), go to about:config, accept the warning and then search for "keyword". Double click on keyword.enabled to set it to false.

This means if you type "keyword" into your location bar then it will look for a local server called keyword and if it can't find one it will show the server not found error instead of falling back to a web search.

You can still use Smart Keywords (see https://support.mozilla.org/en-US/kb/how-search-from-address-bar) and you can run a web search using the separate search box.