Scrolling to a specific message using mhash key in query string does not work sometimes.

[SebinSong]

Problem

NOTE: it did work for Greg in GIG group but did not work when I tried the same message link on my MacOS and also when tried with the latest master locally, hence the word 'sometimes' in the title.

[Steps to reproduce]

1. Create a group and go to the #general chatroom.
2. Add some messages so the scrollbar appears.
3. Copy one of the message link and try it.
4. The chatroom page does appear but it does not auto-scroll to the target message (but rather scroll to the top) and mhash key in the query string disappears too.

Solution

Find out why this functionality has been lost and fix it.

[taoeffect]

@SebinSong I can verify that this seems to be a Firefox issue. See recent link I posted on Slack to a message in GIG, and open it in Firefox.