PDFjs default pref values can't be set via policy

[mkaply]

Because of the way PDF.js sets default values (async, late in startup), they can't be set by policy.

So if policy tries to override the default value for say cursorToolOnLoad, it doesn't work.

When processing PdfJsDefaultPreferences, there should be a check if the value already exist on the default branch and if so, don't set them.

There's a workaround (user preferences), but it would be better if default could be set.

[Snuffleupagus]

When processing PdfJsDefaultPreferences, there should be a check if the value already exist on the default branch and if so, don't set them.

The "correct" solution would probably be to fix https://bugzilla.mozilla.org/show_bug.cgi?id=1780609 instead, see PR #15209, however that'd require feedback from someone knowledgeable about the Firefox preference system to move forward.

[mkaply]

I'm actually wrong. It was a loading mistake on my end. Policy can set these fine.

I do have to load PdfJsDefaultPreferences explicitly so I know the preference type though.