Talkback needs to be enabled.
The close button is read by the Talkback.
The "X" button with "Share" title are focused and read as "Share button"
Android device:
Fenix version: Firefox Preview Nightly 3/31 #20910606.

It's the same for 'Select Tabs' to save to collection view. The button includes the whole title:
Samsung Galaxy S9+ (Android 8.0.0)
Firefox Preview 4.2.0

This is an accessibility P2. The feature is available and works but is difficult to use because of misleading button labeling. This kind of bug prevents Fenix from being a delightful experience for users with disabilities.
@asadotzler Will a content description of "Close" suffice for both? The action is the same, closing that screen, even though one icon is close and the other is back.
Maybe UX can clarify why there is a difference?
@mcarare Hmm. This is odd. We expected that only the close/back button would be highlighted. The page title should never be included in the selection, unless it’s highlighted separately.
@mcarare I also see what you’re saying about why we sometimes have a back icon, and sometimes it’s close. I agree that it’s inconsistent. Let’s file a new issue for this – something that we want Content Strategy to be aware.
@mcarare Filed #10105.
Verified as fixed on the latest Nightly build 6/3 with Google Pixel 3 (Android 10) following the steps from the description.
The issue described in here is not fixed, the back button isn't highlighted.
@mcarare this will be covered in a different bug?
@sflorean Yes, in https://github.com/mozilla-mobile/fenix/issues/10105.