Mattermost screen reader failure on Firefox

Description

Original report: https://github.com/mattermost/mattermost-server/issues/14621

Firefox 76.0.1 on community-release using JAWS Professional Edition 2020.2004.66 ILM

Repro steps:
If using TAB to navigate to the actual message in the post, JAWS does not read it out.

Observed:
Only dates are read, but not the messages or who sent them. There are no errors or screenshots that can be produced in this situation.

QA Test Steps

None

Mana

None

Assignee

Eric Sethna

QA Assignee

None

Reporter

Amy Blais

Epic Link

None

Fix versions

Mattermost Team

Apps

Sprint

None

QA Testing Areas

None

GitHub Issue

None

Components

None

Severity

None
Configure