URL: https://b2c.518fb.com/ecmobile/travel/step1.do?unionCode=B2C_PACKAGE&unionMenu=B2C_TAA&unionSource=MOBILE
Browser / Version: Firefox 51.0
Operating System: Windows 10
Problem type: Desktop site instead of mobile site

Steps to Reproduce

1. Navigate to: https://b2c.518fb.com/ecmobile/travel/step1.do?unionCode=B2C_PACKAGE&unionMenu=B2C_TAA&unionSource=MOBILE
2. See the reproducible steps in the attached image

Expected Behavior:
After pressing the + button in Step4, I will be able to select a second place as what I can do in Step 3.

Actual Behavior:
After pressing the + button in Step4, a date picker is popped out. I have no way to select a second place as what I can do with Edge and Chrome.

Note: I encountered the same problem with Firefox nightly 56 on MAC.

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