Native Firefox viewer for EU e-invoices: show embedded PDF and XML invoice data side by side

[Joris]

Why

More and more European invoices are sent as structured e-invoice files instead of normal PDFs. These files are often XML-based and may include an embedded PDF version of the invoice.

For most users, this is hard to read. When they open the file, they often see raw XML or need accounting software just to understand what the invoice says.

How

Firefox already has a strong built-in PDF viewer. This could be reused to make e-invoices easier to read.

When Firefox detects a supported e-invoice file, it could show a simple split-screen view:

• one side with the PDF version of the invoice, if available;
• one side with the key XML invoice data shown in plain language.

This would help users quickly check who sent the invoice, what it is for, the invoice amount, VAT, due date and payment details.

What

I propose a native Firefox viewer for UBL-based e-invoices.

The first version could focus on common European e-invoice formats based on UBL and EN 16931, such as Peppol BIS Billing 3.0 and national UBL profiles used in countries like Belgium, the Netherlands, Germany and France.

This would not replace accounting software. It would simply give users a safe, open and browser-native way to read and verify structured invoice files.

Annex: technical approach and specifications

Base approach

Firefox could start with a generic UBL invoice viewer. It does not need to validate every national rule from day one. The first goal would be readability.

Suggested flow:

1. User opens an XML invoice file in Firefox.
2. Firefox detects whether it is a UBL Invoice or CreditNote.
3. Firefox checks whether an embedded PDF is available.
4. Firefox shows a readable invoice view:
   • PDF panel, if an embedded PDF exists;
   • structured data panel with the main invoice fields;
   • optional access to the raw XML for advanced users.

Main data fields to show

• Invoice number
• Invoice date
• Supplier name
• Supplier VAT number
• Customer name
• Customer VAT number
• Invoice lines
• Quantity and unit price
• Amount excluding VAT
• VAT percentage
• VAT total
• Total amount payable
• Due date
• Payment reference
• IBAN or payment details
• Attached or embedded documents

Supported formats and regions

A practical first scope could include:

• UBL Invoice 2.1
• UBL CreditNote 2.1
• Peppol BIS Billing 3.0
• Belgian Peppol / UBL invoices
• Dutch NLCIUS / SI-UBL invoices
• German XRechnung invoices when using UBL syntax
• French UBL EN16931 invoice profiles
• Other EU e-invoice profiles that are based on UBL and EN 16931

Technical references

Official OASIS UBL specifications: 
https://docs.oasis-open.org/ubl/ 

UBL Invoice 2.1 schema: 
https://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-Invoice-2.1.xsd 

UBL CreditNote 2.1 schema: 
https://docs.oasis-open.org/ubl/os-UBL-2.1/xsd/maindoc/UBL-CreditNote-2.1.xsd 

Possible XML detection elements

Firefox could detect supported files by looking at common UBL elements and namespaces, for example:

• Invoice
• CreditNote
• CustomizationID
• ProfileID
• AccountingSupplierParty
• AccountingCustomerParty
• TaxTotal
• LegalMonetaryTotal
• InvoiceLine
• CreditNoteLine
• AdditionalDocumentReference
• EmbeddedDocumentBinaryObject

Why this fits Firefox

This would support open standards, user transparency and interoperability. It would also make Firefox more useful for citizens, small businesses, accountants and public-sector users who receive structured e-invoices but do not always have dedicated invoice software available.

[Jon]

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