I'm still hoping for a fix, or at least please tell me which registry entry is corrupted by the update.

In the meantime, I figured out how to use Firefox safely. I disabled the Mozilla Maintenance Service. Having done that, I was able to start Firefox without getting the poisoned update.

Hi, that is a strange one! Try resetting all the settings: Fix printing problems in Firefox.

If that doesn't do it, try starting in Safe Mode, by holding down Shift when you start Firefox, and see if you can use the printer whilst in Safe Mode: Diagnose Firefox issues using Troubleshoot Mode.

If your question is resolved by this or another answer, please take a minute to let us know. Thank you!

Thanks for responding. I carefully read through both of the KB articles you referenced, and their child articles, but none of them were applicable to this situation. The reason they're not applicable is that they deal with printing problems in Firefox. While it's true that Firefox, along with every other application, fails to print after applying the 12/13/2016 update, there is nothing in the Firefox settings which could possibly affect this. Its a system-wide problem.

As I said in my original post, I suspect that the update sets a registry entry which blocks access to the system Print dialog. Assuming my hypothesis is correct, there are only two ways to address this: either issue a new Firefox update which doesn't corrupt the registry, or tell me which registry entry is corrupted so I can manually fix it myself. If I'm wrong, and there is no printer-related registry entry that is affected by the update, then please explain why not only Firefox but Microsoft Outlook, Microsoft Word, and Adobe Acrobat are unable to print after the update, but all of them can print after the system Restore.

So just to recap - and for the benefit of others.

After a Firefox update, you are unable to print from FF, AND other programs, which you believe is caused by FF making a Registry change in the update.

I can see why you think that, but since you now say that other programs are affected, could you check your firewall and other security programs, in case they are blocking your printer's connection.

If a FF update had blocked all user's printers, we would be inundated with complaints, which isn't the case.

BTW, System Restore can be a 'life saver,' but it can also mess up other programs, including anti-virus and FF!

Your recap is correct.

I've checked my security software, which is ESET Smart Security 9, and Windows Firewall. Both before and after the system Restore, they are reporting full operation, which in the case of ESET means hourly virus definition updates. And by the way, after the first time I applied the Firefox update and experienced the print blockage, I did a full computer virus scan. ESET SS9, which I believe is first-class virus detection, didn't find any issues.

To clarify further, after the system Restore, all programs, including Firefox, are able to print. (When I start Firefox, because the Mozilla Maintenance service is disabled, it now asks permission to update, which I deny, after which the un-updated Firefox starts up and works as expected.)

As for why you are not inundated with complaints: I'm using Windows Vista, which I understand is fast going the way of the dodo. Probably very few Firefox users are still running Vista. Although I have no direct evidence, my assumption is that the registry corruption is specific to Vista. And, it took a lot of effort for me to find this forum. I found the KB articles you referenced easily, in my early searches about this problem, but not the forum. I had almost given up and decided to switch to using Chrome, when I finally discovered this forum. My conclusion is that only people running Vista and using Firefox are affected, most of those are not skilled enough to deduce that the Firefox update caused the problem, and some of them were unable or not sufficiently motivated to find the forum and post to it. If Mozilla issues a new update which addresses this, many Vista users will benefit who never understood why they had the problem in the first place.

It might be worth as a test, disabling your ESET Smart Security, since it sounds more like something is blocking the printer, rather than a virus. It's just possible that it updated to a version that is no longer compatible with Vista at the same time as the FF update.

Other than that, I'm out of ideas, so I've escalated your question, which will draw it to the attention of admins, moderators and top contributors.

Good luck!