Hi,
I usually browse voyager and like to share some funny memes.
I'm used to browsing inside Firefox through wefwef.app there to share I long press an image and click Share as an image.
on PWA I d'ont have share as an image in that menu.
I tried the share button but it just download an image on the phone instead of opening my app of choice with the img.
I'm on android
It's a Firefox thing. The context menu in pwa mode is different from the normal one. This is most likely a bug.
A workaround I sometimes use, is to go to the notification drawer, click the silent pwa notification to copy the URL of the current page, share the copied URL with firefox and finally use the normal context menu.
No there is no way to customize the menu. I found an old bug that mentions adding a share option to the context menu. It is probably worth it to either kick this old bug, mentioning what is still missing, or to create a new bug describing the current issue.
I'm using the PWA on android (with Vivaldi browser) and I just long-press the image and get the share image option... so, I don't know why it doesn't work for you.