Roblox is probably only meant to work with Chromium-based browsers, which Firefox isn't.
Since you mention that it's a configuration issue, can you try using troubleshoot mode and test applying your changes one by one?
A place to discuss the news and latest developments on the open-source browser Firefox.
1. Adhere to the instance rules
2. Be kind to one another
3. Communicate in a civil manner
If you would like to bring an issue to the moderators attention, please use the "Create Report" feature on the offending comment or post and it will be reviewed as time allows.