URL: https://discordapp.com/

Browser / Version: Firefox 60.0
Operating System: Linux
Tested Another Browser: Yes

Problem type: Something else
Description: Upload Emoji button in Discord does nothing in Firefox
Steps to Reproduce:
It is impossible to upload emoji to Discord using Firefox.

Steps to reproduce

1. In a web browser, visit https://discordapp.com/
2. Create an account (or log in if you have one)
3. Verify your email address if necessary
4. Create a server (or be given Upload Emoji privilege on a server)
   (N.B. "server" is the term that Discord's UI refers to a guild.)
5. In the first column (list of server icons), open your server
6. At the top of the second column (channel list), click the server name
7. Choose "Server Settings"
8. In the list of sections at left, switch to "Emoji"
9. Click "Upload Emoji"

Result in Chromium:
File chooser appears

Result in Firefox 60 ESR or Firefox 65:
File chooser fails to appear, and nothing is logged in error console

When I reported this problem to Discord support two years ago, the reply was that the team is aware of the issue but there is no ETA on making "Upload Emoji" compatible with Firefox. Instead, users who wish to upload emoji are expected to download, install, and use a second web browser or the Electron-based desktop application.
https://support.discordapp.com/hc/en-us/requests/1132276

Uploading an image as an attachment to a message works. Uploading emoji to a server does not.

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