Delete all your Tweets for free.
If someone else comes across this issue, please open the browser console and let me know what messages appear after selecting the js file.
I'm encountering the same situation. Here's the message I get after uploading tweets.js. Not sure how long to express deletion for this many tweets to take, so I'm keeping the window open for the rest of the day.
All right, I've dug around a bit more in the browser console, and here's a screenshot of the error message I'm receiving when I try running tweets.js. Could it be interacting with a different extension in Firefox?
Not sure if this script is working. The blue bar appears and you can select the js file no issue, but it doesn't show the progress which I can't tell if it's actually working or not. Instead of the "x deleted" progress indicator it shows the "please select the js file" (can't remember the exact line). However, the console method works fine so far.