Cannot assign milestone or label to new issue as I create the issue, in Firefox

Summary

I'm unable to create a new issue and assign a label or assign a milestone to it at the same time. I am running the latest version: 9.3.4-ee

Problem only exists in Firefox. Chrome doesn't show the same issue.

Steps to reproduce

Create a new issue, scroll to the bottom to the milestone or label selection. Try to find existing milestone or labels. No results are presented.

What is the current bug behavior?

The list of milestones and labels are blank. I try to search for milestones or labels that I know exist, but nothing is presented. If you create the issue without assigning a milestone or label, then go back to edit the issue, you can now assign milestones and labels.

What is the expected correct behavior?

I should see a list of existing milestones and labels.

Relevant logs and/or screenshots

Screenshot of label/milestone bug

Results of GitLab environment info

Expand for output related to GitLab environment info 
System information
System:		Ubuntu 16.04
Proxy:		no
Current User:	git
Using RVM:	no
Ruby Version:	2.3.3p222
Gem Version:	2.6.6
Bundler Version:1.13.7
Rake Version:	10.5.0
Redis Version:	3.2.5
Git Version:	2.13.0
Sidekiq Version:5.0.0
Go Version:	unknown


GitLab information
Version:	9.3.4-ee
Revision:	18e7e91
Directory:	/opt/gitlab/embedded/service/gitlab-rails
DB Adapter:	postgresql
DB Version:	9.6.3
URL:		https://git.patrocinium.com
HTTP Clone URL:	https://git.patrocinium.com/some-group/some-project.git
SSH Clone URL:	git@git.patrocinium.com:some-group/some-project.git
Elasticsearch:	no
Geo:		no
Using LDAP:	no
Using Omniauth:	no


GitLab Shell
Version:	5.1.1
Repository storage paths:
  • default: /var/opt/gitlab/git-data/repositories Hooks: /opt/gitlab/embedded/service/gitlab-shell/hooks Git: /opt/gitlab/embedded/bin/git

Results of GitLab application Check

Expand for output related to the GitLab application check 
Checking GitLab Shell ...


GitLab Shell version >= 5.1.1 ? ... OK (5.1.1)
Repo base directory exists?
default... yes
Repo storage directories are symlinks?
default... no
Repo paths owned by git:root, or git:git?
default... yes
Repo paths access is drwxrws---?
default... yes
hooks directories in repos are links: ...
2/1 ... ok
2/2 ... ok
2/3 ... ok
2/4 ... ok
2/5 ... ok
4/6 ... ok
2/7 ... ok
2/8 ... ok
2/9 ... ok
4/10 ... ok
4/11 ... ok
4/12 ... ok
2/13 ... ok
4/14 ... ok
2/15 ... ok
4/16 ... ok
2/17 ... ok
4/18 ... ok
4/19 ... ok
2/20 ... ok
4/21 ... ok
4/22 ... ok
2/23 ... ok
4/24 ... ok
2/25 ... ok
4/26 ... ok
2/27 ... ok
2/28 ... ok
2/29 ... ok
4/30 ... ok
2/31 ... ok
4/32 ... ok
4/33 ... ok
2/34 ... ok
2/35 ... repository is empty
4/36 ... ok
2/37 ... ok
2/38 ... repository is empty
4/39 ... ok
4/40 ... ok
2/43 ... ok
4/44 ... ok
4/46 ... repository is empty
4/47 ... repository is empty
4/48 ... ok
4/49 ... ok
Running /opt/gitlab/embedded/service/gitlab-shell/bin/check
Check GitLab API access: OK
Access to /var/opt/gitlab/.ssh/authorized_keys: OK
Send ping to redis server: OK
gitlab-shell self-check successful


Checking GitLab Shell ... Finished


Checking Sidekiq ...


Running? ... yes
Number of Sidekiq processes ... 1


Checking Sidekiq ... Finished


Checking Reply by email ...


Reply by email is disabled in config/gitlab.yml


Checking Reply by email ... Finished


Checking LDAP ...


LDAP is disabled in config/gitlab.yml


Checking LDAP ... Finished


Checking GitLab ...


Git configured correctly? ... yes
Database config exists? ... yes
All migrations up? ... yes
Database contains orphaned GroupMembers? ... no
GitLab config exists? ... yes
GitLab config up to date? ... yes
Log directory writable? ... yes
Tmp directory writable? ... yes
Uploads directory exists? ... yes
Uploads directory has correct permissions? ... yes
Uploads directory tmp has correct permissions? ... yes
Init script exists? ... skipped (omnibus-gitlab has no init script)
Init script up-to-date? ... skipped (omnibus-gitlab has no init script)
Projects have namespace: ...
2/1 ... yes
2/2 ... yes
2/3 ... yes
2/4 ... yes
2/5 ... yes
4/6 ... yes
2/7 ... yes
2/8 ... yes
2/9 ... yes
4/10 ... yes
4/11 ... yes
4/12 ... yes
2/13 ... yes
4/14 ... yes
2/15 ... yes
4/16 ... yes
2/17 ... yes
4/18 ... yes
4/19 ... yes
2/20 ... yes
4/21 ... yes
4/22 ... yes
2/23 ... yes
4/24 ... yes
2/25 ... yes
4/26 ... yes
2/27 ... yes
2/28 ... yes
2/29 ... yes
4/30 ... yes
2/31 ... yes
4/32 ... yes
4/33 ... yes
2/34 ... yes
2/35 ... yes
4/36 ... yes
2/37 ... yes
2/38 ... yes
4/39 ... yes
4/40 ... yes
2/43 ... yes
4/44 ... yes
4/46 ... yes
4/47 ... yes
4/48 ... yes
4/49 ... yes
Redis version >= 2.8.0? ... yes
Ruby version >= 2.3.3 ? ... yes (2.3.3)
Git version >= 2.7.3 ? ... yes (2.13.0)
Active users: ... 9
Elasticsearch version 5.1 - 5.3? ... skipped (elasticsearch is disabled)


Checking GitLab ... Finished

Possible fixes