Features/Desktop/64bit Firefox Windows 7

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Add support for 64-bit Firefox Windows 7/Vista
Stage Definition
Status `
Release target `
Health OK
Status note `


Product manager Asa Dotzler
Directly Responsible Individual `
Lead engineer `
Security lead `
Privacy lead `
Localization lead `
Accessibility lead `
QA lead Mihaela Velimiroviciu
UX lead `
Product marketing lead `
Operations lead `
Additional members `

Open issues/risks

  • Plug-in support will be a major issue here. We do not want users to have a worse view of 64-bit builds than they do of 32-bit.
  • Accessibility support will be an issue here. Some of the ATs inject their own DLL into Firefox's address space. That would break if they inject a 32-bit DLL into a 64-bit process.
  • Not sure what to do if users have both 32-bit and 64-bit Firefox installed

Stage 1: Definition

1. Feature overview

Offering a x86 64-bit Firefox to Windows 7 (and Vista) 64-bit users brings one immediate and major improvement. It would help dramatically with OOM crashes due to address space exhaustion. There are potential performance benefits as well -- especially in JavaScript land.

This feature falls primarily in the Experience category (from the "Discover, Experience, and Connect" vision statement.)

2. Users & use cases

Users with 64-bit Windows 7 (and Vista) can currently use Firefox 32-bit builds and that's what we offer them. But the 32-bit builds can only use part of the user's memory address space and so we are not taking full advantage of the user's platform capabilities.

3. Dependencies

  • Platform engineering resources are needed to implement running 32-bit plug-ins in 64-bit Firefox.
  • Rel Eng will need to update systems for build, automation, and updating.
  • QA will have one more platform to test.

4. Requirements

  • Coherent 32 bit plugin on 64-bit build experience
  • Build automation able to create 64 bit builds
  • QA automation able to test 64 and 32-bit builds
  • AUS changes to support 64 and 32-bit builds and updates
  • www.mozilla.com to offer 64-bit builds
  • Performance parity with 32-bit Firefox on Windows
  • Stability parity with 32-bit Firefox on Windows


  • We should not attempt support of 64-bit Windows XP (neither x86-64 nor Itanium)
  • We do not immediately need a stub installer or website magic to deliver 64-bit builds to 64-bit Windows users.
  • We do not need or expect memory use parity with 32-bit Firefox.
  • We do not intend to drop support for 32-bit Firefox.

Stage 2: Design

5. Functional specification


6. User experience design


Stage 3: Planning

7. Implementation plan


8. Reviews

Security review


Privacy review


Localization review




Quality Assurance review


Operations review


Stage 4: Development

9. Implementation

Stage 5: Release

10. Landing criteria


Feature details

Priority P2
Rank 999
Theme / Goal Experience
Roadmap Firefox Desktop
Secondary roadmap `
Feature list Desktop
Project `
Engineering team Plugins

Team status notes

  status notes
Products ` `
Engineering ` `
Security ` `
Privacy ` `
Localization ` `
Accessibility ` `
Quality assurance ` `
User experience ` `
Product marketing ` `
Operations ` `