Thank you for sharing this, as I'm sure the developers will be interested. My understanding is that DA WCAG applies to websites, not to email clients, but I'm not well-versed in this. You will help us if you will point to the compliance standards requirements that affect threading. This is the support forum, but I assure you that such information, once you provide it, will be forwarded to appropriate personnel. Thank you.

The WCAG and ADA standard does not specify threading. It relates to creating changes that require having pre- knowledge and knowing multiple steps to find accessible functions. The need to do multiple steps for every folder is the barrier. If there was a one-step process for each folder, that would likely be in compliance. The critical part is the solution is not obvious. One needs to know that the solution is in the View part of the Menu options, then Sort By (when the Threads option looks obvious but does not lead to a solution) then finally Unthread. To start the whole process, one must KNOW, Have preknowledge, that those three short horizontal bars as an icon lead to a Menu. WCAG requires the solution to have an obvious path. A right click on a folder with Threading options would be appropriate. Instead, the options are divided into may different multi-step paths. WCAG requires an option for "Text under an Icon". Not just "Hover and text will show up" Many have no idea that those three short horizontal bars mean anything. Mozilla deleted these options about 4 or 5 years ago. We have a large population of ASD, Autism Spectrum Disorder, who may be literal thinkers and others who have inabilities to memorize processes that are not obvious or an inability to translate Icons into a text based concept. These fancy threading functions should be the options, not the default.

Thank you for the detailed write-up. I will be sure to forward this entire text to those in a position to make decisions. This forum is administered by volunteers and we have no such authority on what features to add or change. Again, thank you.

If interested, you can follow the review at https://bugzilla.mozilla.org/show_bug.cgi?id=1829737 or offer your input there as you see appropriate. This is the limit of what support is available to you on this support forum.