I was able to create widgets less than a week ago, but now I can't

Nothing on my computer has changed since the last time I created widgets, literally just a few days ago. I'm not sure why it's suddenly not working.

What's up? For example, for the subreddit widget I'm able to type in the subs and the display name, but when I go to click the ADD button, nothing happens. Tried to make a search widget as well and the same thing happens. I tried experimenting with an existing subreddit widget and went to add another sub. Clicked SAVE and it looks like it's saving, but the sub wasn't actually added.

Where does it happen? Dashboard

What browser extensions are installed? I disabled all of them and tried again. Same thing happened.

• Night mode: false
• RES Version: 5.6.1
• Browser: Firefox
• Browser Version: 52
• Cookies Enabled: true
• Reddit beta: false