Bad news: It's worst that Deluminate in Chrome!
Long story: I've done some intensive testing on all available add-ons in FF (and chrome). There are about 5-6 "night readers" on each. In general, the "inverters" in FF (unlike chrome) are all a bit worse in tems of not breaking the websites (i.e unusable for default browsing). So the only solution is to use a "themer", the best of which is this (Check Theme 10)! And if you need additional contrast, apply an inverter on top of it (It works (eg. Aniverto)! Or a web-site specific themer, It also works (eg. Black Google)! If you don't like this due to low contrast, your only other real option is to use "Screen Dimmer" but this is way better and in my experience it is the ONLY viable alternative in FF. Without it, I would have no option but to revert to chrome. So, thank you dev!
PS. If you can do the impossible and increase font brightness a bit or at least do some magic with the plague of "bright flashes on loading" (that plague both chrome and FF for ages!) that would be 5+ stars!! Ratings are based on eye-strain!!