UserAgent: Mozilla/5.0 (Windows NT 6.0; rv:52.0) Gecko/20100101 Firefox/52.0

Example URL:
https://github.com/gentilkiwi/wanakiwi

Steps to reproduce the problem:
Unfortunately I don't know of a way to reproduce this. I have seen this before but rarely. The steps taken were:
1. https://github.com/gentilkiwi/wanakiwi in Private Browsing
2. Click on the link icon next to 'Frequently Asked Questions', observe #frequently-asked-questions is appended in location bar
3. Click on 'inc/openssl' folder, observe it's opened
4. Click back button, expecting to return to #frequently-asked-questions. Observe location bar updates with this URL but the contents doesn't change back.
5. Click back again, observe you're back at original wanakiwi page.
6. Click forward, observe #frequently-asked-questions.
7. Click forward again, observe inc/openssl
8. Click back, observe same problem as #4.

What is the expected behavior?
The back button should always work correctly.

What went wrong?
Moving back may not change page. See animated GIF for example.

Does it occur on multiple sites: Yes

Is it a problem with a plugin? No 

Did this work before? N/A 

Does this work in other browsers? Yes

Chrome version: Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.96 Safari/537.36  Channel: stable
OS Version: Windows 7
Flash Version:
 

Deleted: back button doesn't always work.gif 167 KB

	back button doesn't always work.gif 167 KB View Download