Try using a large blocklist[1] in your hosts file and installing umatrix[2] and/or ublock origin[3] to block garbage scripts from loading. I don't know if that will help, but that's what I'm doing and Firefox is as fast or faster than Chrome.
I confess that I have uMatrix in Chrome but not FF, but I do use pihole, and it’s not really a third party scripts problem, FF feels slower on perfectly clean sites.
Maybe it has something to do with the combination of your OS and Firefox versions. I've just tested a few sites (without umatrix, but with Firefox's built-in privacy protection) and they are about the same speed according to the network console. Sometimes Firefox is slightly faster, other times Chrome is slightly faster. (Ubuntu 16.04)
I have performance issues with heavy sites because I use many extensions. Sometimes, I disable all extensions and it stills sluggish on Facebook for example, but the issue goes away when I use a new profile. Maybe you can try it.
[1] https://www.google.com/search?q=hosts+blocklists
[2] https://addons.mozilla.org/en-US/firefox/addon/umatrix/
[3] https://addons.mozilla.org/en-US/firefox/addon/ublock-origin...