You are using Firefox Beta. There is an option to disable the check, but it will be removed in Firefox 42. So you will have a limited time of being able to use unsigned add-ons in Firefox beta and release. You will need to use Nightly, Dev Edition or the soon to be released unbranded version of release to use unsigned add-ons.

It's better to check and make sure there are no updates to your add-ons (that might be signed already) and then bug the developers to sign their add-ons (a simple, automatic process)

Firefox 40: Firefox warns about signatures but doesn't enforce them. Firefox 41: Firefox will have a preference that allows signature enforcement to be disabled (xpinstall.signatures.required in about:config). Firefox 42: Release and Beta versions of Firefox 42.0 will not allow unsigned extensions to be installed, with no override

Since you are Testing the Beta builds of Firefox 41.0 on Beta channel you are seeing this change sooner.

See also:

• https://wiki.mozilla.org/Addons/Extension_Signing

lol your company think your users too stupid to decide by their own what extension to use? I suggest you to change your mind, I will lose at least one user because of it. Anyway, thanks for help

I have non-open source plugins written by my company distributed only internally to the company. How are we meant to handle that situation?

http://www.palemoon.org/ allows installing some plugins that have not been signed. YMMV.

There are a few things you can do. You can install Firefox nightly or Dev edition, which allow unsigned extensions, or use the unbranded versions of beta or release that come out in a few weeks, which will allow unsigned extensions. Firefox release currently warns about signed add-ons, but doesn't disable them. That will change in 41.

My unsigned addons are disabled in 40.0.3, no option to turn them on. I also loose access to the data in the plugins. Moving to a different FireFox will not get me my data back.

It stinks this; just because Apple have a militant stance on using their APP Store, does not mean open source projects should follow suit. What happened to "FireFox does good". Mozilla want you using their own App store and don't want competition. Its not about security , cause I wrote the code.

Can you please post a screenshot of your addons screen? 40.0.3 doesn't disable unsigned add-ons, so I'm wondering what you are seeing exactly.

And yes, installing a version of Firefox that allows you to run unsigned add-ons will use your same profile (except dev edition) so it will be just like signing never happened.

We don't want you using our App Store if it doesn't work for you, but we don't want the millions of users out there being plagued by malicious add-ons to have to suffer. We've done the best we can to make signing easy for developers, and you can get your add-ons signed even if they are private ones only you will ever use. https://wiki.mozilla.org/Addons/Extension_Signing for more details.