I recently started using firefox as well as chrome and I can do everything but the actual projects, it says I need a plugin for it but I don't know what plugin.
I was wondering if anyone knew what I needed to install? Thanks

It's already installed - shockwave flash. Open Firefox, and in the address bar, type in about:addons. Go to the Plugins tab on the left and find “Shockwave Flash”. On the right, click on the menu and select “Always activate”. That should do it.

Thanks! I don't seem to have it though, but I'll try installing it and see if that works

I have the same problem. An empty page load instead of the online editor on my Windows 10 firefox machine. There is no Shockwave at the plugins neither one to download. I tried to install it from the official site https://get.adobe.com/shockwave/ but when I clicked on the download button it redirected me to https://www.adobe.com/# .

Instead I download and install the flash player https://get.adobe.com/flashplayer/ and it worked after it asked me if I want to load it!