Developer reply by Jeremy Gregorio
Rated 1 out of 5 stars
It no longer works on Youtube. It was powerful and easy to use. It supported several formats, editing metadata, and clipping the beginning and end. I loved it. I contributed and will contribute generously again once it is fixed. I'll change my rating too of course.
While it's hardly idea you should be able to get the plugin working again by disabling e10 (aka multiprocess). Go to about:config, search for browser.tabs.remote.autostart and set it to false. You might also need to set browser.tabs.remote.force-enable to false if you have it. Then restart Firefox.
To check if it worked Go to about:support and you should see an item called "Multiprocess Windows" set to 0/1.
I'm hoping to get some time later this year to work on e10 support, but it's a pretty major upgrade. My UI has to be completely re-written and there's a ton of work to do to make it all fit together.
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