I want use Google autocomplete in the search bar (not search box) of Firefox, like in Google Chrome.
As of Firefox 43, autocomplete for any search engine is available from the location bar.
I've searched for this myself in the past and would also like this feature. As of Firefox 38.0.1, there is no way to do this just as you ask.
Two alternatives (just in case you don't know them already):
- Using the dedicated search box and enabling the search suggestions checkbox in the options menu
- Using an addon like Omnibar, Instantfox, or Foobar.
Since you like search suggestions, a simple solution is to used InstantFox.