xpinstall.signatures.required preference to stay in Fireofx 44  & 45, but will be removed from Firefox 46.As per the announcement made by Mozilla earlier, Firefox 44 stable, doesn’t allow the install of unsigned add-ons, and the preference xpinstall.signatures.required should not be available in about:config for users to change.

This has been changed, the company has reconsidered their decision and isn’t going to remove the preference till Firefox 46. Means, the preference will exist in stable and beta version of Fiefox 44, and Firefox 45, and you can be able install unsigned extensions in them without any trouble.

xpinstall signature required preference present in Firefox 44

The bottom line is Release and beta versions of Firefox 46 won’ t allow unsigned extensions to be installed, with no override (preference won’t be available, but it will be in Nightly and developer channels).

Mozilla has taken this decision to give developers more time to sign their add-ons, and also they want the preference to available even in Firefox 45, which allows devleopers to temporarily test restartless unsigned add-ons.