What's your computer system and Firefox version?

This may be your problem,

Firefox v52+ disables all plugins except for Flash Why do Java, Silverlight, Adobe Acrobat and other plugins no longer work? {web link}

Install Older Version Of Firefox {web link} Be sure to read everything here.

If you still want to downgrade, look under; I still want to downgrade. Click the Directory of other versions and languages link. Look for the directory of the version that you want. But, remember that old versions may have security issues.

You should also check out Firefox; Extended Support Release {web link} ESR Notes System Requirements

My computer is running Windows 7 and FF 53.0.2.

The computer meets the "System Requirements," but there is no mention of external hardware requirements that require the older, NPAPI plugins.

From the Firefox: Extended Support Release link, Mozilla seems to be leaving behind Individuals would have "older" hardware1 that does not support the newer browser platform/ NPAPI less platform. The ESR is designed for enterprise systems and large system deployment.

The selection of web browsers is dwindling. Chrome has not supported NPAPI for awhile and Safari for windows has not seen an upgrade for years. The choice seems to be run Internet Explorer 11 or FireFox before V52.

My understanding from the questions is: there was no effect by changing "accessibility.AOM.enabled" and that there is no about:config reference. Thank you for the information and suggestions. I'm very surprised, and disappointed, that Mozilla doesn't provide about:config documentation. I'll be a more educated consumer when talking to the camera manufacturer.

1. The camera, purchased Oct 2015, is now useless.- the manufacturer has the ability to fix the problem.

> Mozilla doesn't provide about:config documentation.

There are THOUSANDS of prefs currently in Firefox that get added / removed in each Firefox version and having a constantly changing list of prefs is a lot of work. There is a list (not exhaustive) available on Mozillazine that lists prefs but I am not sure how current it is.

• http://kb.mozillazine.org/About:config_entries
• http://kb.mozillazine.org/About:config

Moses said

> Mozilla doesn't provide about:config documentation.

This add-on shows some of the descriptions, but not all of them.

https://addons.mozilla.org/en-US/firefox/addon/config-descriptions/ Config Descriptions Shows source comments for advanced application preferences in about:config

In   'about:config'   the preference :

accessibility.AOM.enabled   has it's value set to   false   by default.

Happy112, FredMcD, Moses,

  Thank you for the information.  accessibility.AOM.enabled was not found but many other preferences descriptions are available on MozillaZine - that will be a good reference.  I've reset the preference back to the original setting and better armed to contact tech support again. 
  I really appreciate the info.

Glad to help. Safe Surfing.

That is part of the accessibility object model (AOM) that deals with for instance screen readers interacting with website content.

• https://wiki.mozilla.org/Accessibility/WebAccessibilityAPI

See Depends on under Tracking for additional bugs if you are interested.

• Bug 1313691 - implement AOM

cor-el,

     I'm aware of AOM, after reading some  and realized that the camera technical support ask me to change something that should have had nothing to do with the camera.     "Happy 112" pointed out the default setting is false, which is the setting that was changed to the same value.  I've not cleared up the camera issue but understand Firefox better and know better where to look for assistance. 
    Thank you.

Your question was :

"What effect will disabling accessibility.AOM.enabled have on Firefox? "

The answer is : None,   as it is disabled by default ,   see : In 'about:config' the preference : accessibility.AOM.enabled has it's value set to false by default.

You say that you have not 'cleared up the camera issue'   -   what exactly is that issue   ?