There seems to be the following workaround:
You can turn-off hardware-acceleration in Firefox: options > advance > general
If that doesn't work, it's simply a compatibility issue, and I would contact the developers to update their plugin.
If you need something like DOM Inspector, why not use Firebug instead?
The most popular and powerful web development tool:
- Inspect HTML and modify style and layout in real-time
- Accurately analyze network usage and performance