Copy table using Selenium and Python
First off, I see a couple of things that can be shortened to generator expressions, rather than full-blown for loops. For example, this section:

file_header = []
head_line = head.find_element_by_tag_name('tr')
headers = head_line.find_elements_by_tag_name('th')
for header in headers:
    header_text = header.text.encode('utf8')
    file_header.append(header_text)
file_data.append(",".join(file_header))


Can be shortened immensely  to the following:

head_line = head.find_element_by_tag_name("tr")
file_header = [header.text.encode("utf8") for header in head_line.find_elements_by_tag_name('th')]
file_data.append(",".join(file_header))


Finally, your other for loop can be shortened to a generator expression as well. For more on generator expressions, see PEP0289.