Python/Selenium - Can only set cookies in the current domain

I am receiving an error which says: You may only set cookies for the current domain when trying to perform a login. The accompanying message is:

    selenium.common.exceptions.WebDriverException: Message: You may only set cookies for the current domain
Stacktrace:
    at FirefoxDriver.prototype.addCookie (file:///var/folders/28/wvky4dzs7jjfz98kvhdws0qw0000gn/T/tmpirpr_55b/extensions/fxdriver@googlecode.com/components/driver-component.js:10880)
    at DelayedCommand.prototype.executeInternal_/h (file:///var/folders/28/wvky4dzs7jjfz98kvhdws0qw0000gn/T/tmpirpr_55b/extensions/fxdriver@googlecode.com/components/command-processor.js:12661)
    at DelayedCommand.prototype.executeInternal_ (file:///var/folders/28/wvky4dzs7jjfz98kvhdws0qw0000gn/T/tmpirpr_55b/extensions/fxdriver@googlecode.com/components/command-processor.js:12666)
    at DelayedCommand.prototype.execute/< (file:///var/folders/28/wvky4dzs7jjfz98kvhdws0qw0000gn/T/tmpirpr_55b/extensions/fxdriver@googlecode.com/components/command-processor.js:12608)

I run this segment earlier in the script:

for cookie in session.cookies:
driver.add_cookie({
    'name': cookie.name,
    'value': cookie.value,
    'path': '/',
    'domain': cookie.domain
})

This transfers the cookies from a requests.Session() to a Selenium webdriver object so some JavaScript can be executed on the target page.

When I print all these cookies out, all the domains match the target.

How can I get rid of the error? I have absolutely no idea what may be causing it.