Bugzilla

I can reproduce the blank pages on macOS if I do the following using a build from BEFORE bug 1665904 landed on Sept 20th:

Open Firefox with a new profile, disable the new print UI by setting `print.tab-modal.enabled = false`. (I don't have a way to repro with the new UI yet.)

Additionally add exactly the following four prefs, paying attention to add them with the specified types:

```
user_pref("print.print_paper_size_unit", 1);     // number
user_pref("print.print_paper_name", "iso_a4");   // string
user_pref("print.print_paper_width", "210.00");  // string
user_pref("print.print_paper_width", "297.00");  // string
```

Then print, which opens the system print dialog, and select PDF -> Open in Preview.

We then end up with the value from `print.print_paper_size_unit` being copied onto the equivalent pref for the printer that was selected by default in the system print dialog (so `print.printer_<printer>.print_paper_size_unit`) which is the printer the settings come from for the PDF generation, causing the paper settings for that printer to be busted with the incorrect unit.

I can reproduce the blank pages on macOS if I do the following using a build from BEFORE bug 1665904 landed on Sept 20th:

Open Firefox with a new profile, disable the new print UI by setting `print.tab-modal.enabled = false`. (I don't have a way to repro with the new UI yet.)

Additionally add exactly the following four prefs, paying attention to add them with the specified types:

```
user_pref("print.print_paper_size_unit", 1);     // number
user_pref("print.print_paper_name", "iso_a4");   // string
user_pref("print.print_paper_width", "210.00");  // string
user_pref("print.print_paper_height", "297.00");  // string
```

Then print, which opens the system print dialog, and select PDF -> Open in Preview.

We then end up with the value from `print.print_paper_size_unit` being copied onto the equivalent pref for the printer that was selected by default in the system print dialog (so `print.printer_<printer>.print_paper_size_unit`) which is the printer the settings come from for the PDF generation, causing the paper settings for that printer to be busted with the incorrect unit.

I can reproduce the blank pages on macOS if I do the following using a build from BEFORE bug 1665904 landed on Sept 20th:

Open Firefox with a new profile, disable the new print UI by setting `print.tab-modal.enabled = false`. (I don't have a way to repro with the new UI yet.)

Additionally add exactly the following four prefs, paying attention to add them with the specified types:

```
user_pref("print.print_paper_size_unit", 1);     // number
user_pref("print.print_paper_name", "iso_a4");   // string
user_pref("print.print_paper_width", "210.00");  // string
user_pref("print.print_paper_height", "297.00"); // string
```

Then print, which opens the system print dialog, and select PDF -> Open in Preview.

We then end up with the value from `print.print_paper_size_unit` being copied onto the equivalent pref for the printer that was selected by default in the system print dialog (so `print.printer_<printer>.print_paper_size_unit`) which is the printer the settings come from for the PDF generation, causing the paper settings for that printer to be busted with the incorrect unit.