[orca-list] firefox: orca ignore image link without name in navigation mode

[Jérémy Prego <jeremy pregonetwork net>]

hello,

firefox 52.9.0esr and 69.0 esr
chromium dev

since the commit 691f4607d5892932cfdfa9202d262c10c35b3dd5 (    Don't
present image children of links if the image lacks an explicit name), in
browse mode, orca ignores the link of the image that have no label when
I use firefox. I can go on the link with the tab key, but if I don't
know that a picture without a name is present on the page, I think that
there is a missing information.

however,, with chromium, I have the link in the navigation mode. orca
only says "link", but at least I can see it and click it, without having
to pass by the tab key.

example of a message with a link: 
https://lafibre.info/bistro-sujet-libre/frais-de-tenue-de-compte/msg767823/#msg767823

the link is located just after: "(cliquez sur la miniature ci-dessous -
le document est au format PDF)".

thanks for the correction if possible !

Jerem