Expose prefs for tabs-on-demand

Summary

• Firefox 4 has the hidden ability to load tabs on-demand by setting the maximum number of concurrent tabs being restored to "0" — now that the feature has been in the wild for a while, we'd like to expose it as the default behavior for session restore. It makes startup a lot faster, and uses a lot less memory.
• This feature falls primarily in the Experience category (from the "Discover, Experience, and Connect" vision statement.)
• This feature is available starting Firefox 8.

Reference

• Feature wiki page - Link

Use Cases to Test

• Start Firefox when option is disabled
• Start firefox when option is enabled
• Use multiple tab groups
• Start firefox with app tabs
• Load pages with form data
• Restore with no network
• Change options duing loading
• Start Firefox with many tabs open
• Multiple windows

Test Cases

• The set of testcases can be found here

Important bugs

• Implementation bug: 648683 - Expose tabs on-demand preference - VERIFIED FIXED

• Other bugs:
  • 699223 - Change of "Don't load tabs until selected" pref is applied in the same session - NEW (normal)
  • 696106 - "Don't load tabs until selected" pref is applied for all startup options at restart - NEW (minor)

Sign Off Criteria

• No major/critical bugs open
• Test run coverage: 100%

Note:

• Signed off on Firefox 8.0 beta 6 (build ID: 20111031184046)