The difference is that you cannot use a packaged Chrome browser; you need a special driver... chromedriver.

Get the current latest version here: Chromedriver

Now you have 2 options, either to move the downloaded chromedriver so it is always accessible (option 1), or to define in your script how to access it.

Option 1: move it into path

Then move it so it is accessible when you use webdriver.Chrome():

sudo mv /path/to/download/chromedriver /usr/bin

Also set it to be allowed to be executed:

chmod a+x /usr/binchromedriver

Option 2: do not move it into path

Or you can define a path

import os
chr = "/Users/you/Downloads/chromedriver"
os.environ["webdriver.chrome.driver"] = chr
driver = webdriver.Chrome(chromedriver)

(Note: the original question was about Chrome, so my answer is about Chrome, not Firefox).

For me it works if I just extract the chromedriver into the same folder where the script is.

Then I run it as this

Xvfb :99 -ac -screen 0 1280x1024x16 &
echo 'Starting the test'
PATH=$PATH:. python selenimum_scrape.py

This will start the Xvfb and include the cromedriver into PATH.

And the modified version of your which works for me:

import os
import time
from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
from selenium.common.exceptions import TimeoutException

# comment this out to run on the real display
os.environ['DISPLAY'] = ':99'

def init_driver():
    driver = webdriver.Chrome()
    driver.wait = WebDriverWait(driver, 5)
    return driver

def lookup(driver, query):
    driver.get("http://www.google.com")
    try:
        box = driver.wait.until(EC.presence_of_element_located(
            (By.NAME, "q")))
        # once we type the query, this button disappears
        # button = driver.wait.until(EC.element_to_be_clickable(
        #     (By.NAME, "btnK")))
        box.send_keys(query)
        button = driver.wait.until(EC.element_to_be_clickable(
            (By.NAME, "btnG")))
        button.click()
    except TimeoutException:
        print("Box or Button not found in google.com")

if __name__ == "__main__":
    driver = init_driver()
    lookup(driver, "Selenium")
    time.sleep(5)
    driver.quit()

The question is (at the moment) about an indentation error. This can be easily fixed:

def lookup(driver, query):
    driver.get("http://www.google.com")
    try:
        box = driver.wait.until(EC.presence_of_element_located(
            (By.NAME, "q")))
        button = driver.wait.until(EC.element_to_be_clickable(
            (By.NAME, "btnK")))
        box.send_keys(query)
        button.click()
    except TimeoutException:
        print("Box or Button not found in google.com")