Not compatible with current version of Firefox

[AurorWalnut]

Firesheep isn't working with firefox 48, and upon downgrading to firefox 45.0.6 it remained incompatible. Firefox dev addition didn't work either. All had xpinstall.signatures.required set to false, so it was simply a compatibility issue. What version does it work with?

[jeanbza]

Same problem

[crypt3r2]

You need an earlier version of FireFox. It says FireFox 3.6.12 or newer is required, but this was way back in the days, not as new as 48 or 45. You need to go back to FireFox 3.7.* and newer (FireFox 4.* Beta is not supported as stated on https://codebutler.github.io/firesheep/)