Always focus the viewerContainer when entering PresentationMode (bug 1787456)

[Snuffleupagus]

This fixes the regression in bug 1787456, assuming that it should be handled on the PDF.js side.

[Snuffleupagus]

/botio-linux preview

[pdfjsbot]

From: Bot.io (Linux m4)

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Received

Command cmd_preview from @Snuffleupagus received. Current queue size: 0

Live output at: http://54.241.84.105:8877/0ccb7af79214e1e/output.txt

[pdfjsbot]

From: Bot.io (Linux m4)

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Success

Full output at http://54.241.84.105:8877/0ccb7af79214e1e/output.txt

Total script time: 2.16 mins

Published

• Viewer: http://54.241.84.105:8877/0ccb7af79214e1e/web/viewer.html
• Viewer (legacy): http://54.241.84.105:8877/0ccb7af79214e1e/legacy/web/viewer.html

[calixteman]

Don't you think that, in general, the buttons shouldn't steal the focus ?
Anyway, the other buttons grab the focus when they're clicked but the keyboard callbacks are correctly executed, so there is something specifically wrong with the fullscreen mode.

[Snuffleupagus]

Don't you think that, in general, the buttons shouldn't steal the focus ?

That might depend on the exact circumstances, since they definitely need to do that when using a keyboard. When using a mouse, I suppose that in general it may or may not be what you want depending on the exact situation.
Trying to handle both the mouse and keyboard correctly may be difficult/messy, I don't really know, so probably not something we want to worry about here (or even at all)...

Anyway, the other buttons grab the focus when they're clicked but the keyboard callbacks are correctly executed, so there is something specifically wrong with the fullscreen mode.

Yes, this is specifically a regression in Firefox related to Fullscreen-mode (as mentioned in the bug). However, based on https://bugzilla.mozilla.org/show_bug.cgi?id=1787456#c6 it seems that we should take this patch since it's very simple and should also be safe to uplift.

[calixteman]

LGTM.