I have installed a Firefox plugin many years ago that used Greasemonkey to allow to show editor and previewer panels side by side on MathExchange (maybe other Exchanges as well).
After I reset Firefox I lost it and have been trying to search it for longer than two hours and I can't find it. I found a few posts on SE meta on the topic "preview on the right" but those posts are pretty old and are not actually pointing to a solution I was looking for.
Could someone please let me know where I can get it? Thanks.