Easy pass is still working, just not with FireFox 43.x.
Why?
Because Mozilla decided to make changes, not avast.
User where warned that many add-ons would soon not gonna work anymore in FireFox 41.x and 42.x
They had time enough to
- ask Mozilla about certain add-ons, but they didn't.
- search for other add-ons that would work.
- enough to switch to a other browser.
Don't blame the oil company for making the same fuel for years if a car manufacturer decides to put a engine in their cars that can't handle that fuel anymore.
From Mozilla :
Unsigned add-ons can still be installed in Developer Edition, Nightly, and ESR versions of Firefox, after toggling the xpinstall.signatures.required preference in about:config.
The solution is really simple. If you want to use Easy Pass and FireFox, use one of those versions.