Well, i'm not a professional in web browsers but i didn't see extensions in Pale Moon so far
Is a fast, beautiful and really good browser when it comes to daily use, i mostly use it to play Roblox with my friends, use the forum and download stuff since it seems faster here
But i also use Edge when i need to use extensions (like VPN to farm microsoft rewards points or use UTorrent since i defined my account on it on Edge, unfortunately =') ), but my main browser is Pale Moon and i use it way more than any other, since it's perfect if you want something beautiful, fast and easy to use
The only configuration you'll have to do will be on the searching mechanics, since it uses as default the DuckDuckGo but you can switch to Yahoo or Google in the configurations
But in general, is so good if you're someone simple looking for a fast and good browser for low end PCs =)