I think that this is affected to not only Page Info dialog but also the other XUL dialog.
And it needs to migrate XULStore for xhtml file like Bug 1603457.

Reproducible: once update from 20191210095443 to 20191211094640

Steps To Reproduce

1. Start Nightly Build ID 20191210095443
2. Open Page Info dialog(for example)
3. Move the dialog somewhere
4. Quit browser
5. Start Nightly Build ID 20191211094640 with same profile of step1
6. Open Page Info
   --- observe position of the dialog window

Actual Results:
Position of XUL dialog window lost after Nightly update.
Always opened at top-left of screen

Expected Results:
Same position before

Regression window:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=5fd7ad835de62e94f7c6a011671a1eda92ba4ca7&tochange=23c591259da010fe4857703af04a6b90458f91de

The priority flag is not set for this bug.
:bgrins, could you have a look please?

For more information, please visit auto_nag documentation.

Brian, were you able to reproduce this? I can migrate the XUL store for pageInfo and aboutDialog files, but as of right now, I'm seeing the page Info dialog pop up in the same position as before

(In reply to Emma Malysz from comment #2)

Brian, were you able to reproduce this? I can migrate the XUL store for pageInfo and aboutDialog files, but as of right now, I'm seeing the page Info dialog pop up in the same position as before

Yeah, once the page is opened / resized once the problem will go away as the location gets saved with the new URL. We actually have a tricky situation now where if we migrate today then people could lose the settings they saved on the new document. We could mostly mitigate this by checking for the existence of the new document's URL in XULStore - but I think once the window has been opened once it will exist even if the user hasn't moved it around.

Mossop, I was considering wontfixing this, but a patch could certainly be made for 73 beta to prevent this from happening to beta / release users. I'd like a second opinion - how important would it be if a few secondary top level windows (Page Info & About dialog being the most visible) lost their persisted positioning saved in xulstore?

(In reply to Brian Grinstead [:bgrins] from comment #3)

Mossop, I was considering wontfixing this, but a patch could certainly be made for 73 beta to prevent this from happening to beta / release users. I'd like a second opinion - how important would it be if a few secondary top level windows (Page Info & About dialog being the most visible) lost their persisted positioning saved in xulstore?

And to be clear this is a one-time loss, after that the position and size are saved correctly again?

If that is the case then I do not think this is worth much effort to fix (though opening in the middle of the screen rather than top-left would be somewhat preferable). I would support a wontfix.

(In reply to Dave Townsend [:mossop] (he/him) from comment #4)

(In reply to Brian Grinstead [:bgrins] from comment #3)

Mossop, I was considering wontfixing this, but a patch could certainly be made for 73 beta to prevent this from happening to beta / release users. I'd like a second opinion - how important would it be if a few secondary top level windows (Page Info & About dialog being the most visible) lost their persisted positioning saved in xulstore?

And to be clear this is a one-time loss, after that the position and size are saved correctly again?

If that is the case then I do not think this is worth much effort to fix (though opening in the middle of the screen rather than top-left would be somewhat preferable). I would support a wontfix.

Correct - it's a one time loss. It'll be treated as if it was a brand new window (or one that's never been opened).