Contact their support sites. It's up to them to keep the software current.

You are on the beta track, so you are one version ahead of most users.

As you've noticed, Firefox 41 requires that extensions be signed by Mozilla, which follows a brief review process. Presumably the publishers of many of your extensions will take care of that before Firefox 41 is officially released in about 4 weeks.

Would you want to run the current release, Firefox 40.0.2, instead of the beta test release? It doesn't block unsigned extensions. You can grab that here (scroll down to your preferred language): https://www.mozilla.org/firefox/all/

Alternately, you can flip a setting that exists only in Firefox 41 to allow unsigned extensions. That can be found here:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste xpi and pause while the list is filtered

(3) Double-click the xpinstall.signatures.required preference to switch it from true to false

Does one of those suggestions resolve the issue?