Not really as the main protection is the avast Web Shield whilst browsing.
The AOS has some elements that I would say are a bonus, rather than a must have - I have it on this XP/Firefox system - mainly so that I can refer to it if a question is raised in the forums.
I don’t Have Safe Price enabled on either of my systems.
You can remove them from the avastUI > Settings > Components > Security Browser Extension (AOS) and the SafePrice Browser Protection. This will uninstall the modules in your browser/s.
That said I think you are asking a slightly different question, because firefox has both disabled and the AOS not being verified. I don’t know why it isn’t verified or what firefox means by verified, it could be that it hasn’t been signed, but then I would expect the same error for SafePrice.
What avast version are you using (12.3.2280 being the latest version) ?
What firefox version are you using (48.0.2 being the latest regular release) ?
My avast is the latest version just now, and I think it got resolved when I updated my Avast to the latest version. So thank you for your prompt reply. I just thought it was strange that AOS is not enabled in Firefox, but as I’ve said, it’s been resolved now as soon as I downloaded the latest Avast version.