Do you get the "Cannot load tweet. Disable your adblocker and tracking protection." message or just don't see anything at all?
I just checked on a vanilla Firefox (v73, the current version) download and it loads fine.
You should 1) make sure that Firefox is up to date, 2) disable any addons that you have, 3) clear your cache, and 4) check the tracking settings at about
references#privacy
Once you get it working on what is basically a clean install, start turning your addons back on one by one until you figure out what one(s) is/are causing the problem.