Added Firefox Flag for view transitions

[dletorey]

Summary

• Added Firefox Nightly support for:
  • :active-view-transition pseudo-class
  • Document.startViewTransition method
  • viewTranstions API

Test results and supporting details

Tested using this codepen in the following browsers:

• Firefox 140.0.4 - behind flag
• Firefox Beta 141.0 - behind flag
• Firefox Developer 141.0b9 - behind flag
• Firefox Nightly 142.0a1 - supported

Related issues

• previous BCD PR

[github-actions]

Tip: Review these changes grouped by change (recommended for most PRs), or grouped by feature (for large PRs).

[Elchi3]

I think this PR is not needed.
I mean, if it is available in Nightly without a flag, then just setting "preview" is all we need.

[dletorey]

I think this PR is not needed. I mean, if it is available in Nightly without a flag, then just setting "preview" is all we need.

The flag however is needed for Beta & Developer…

[Elchi3]

I see. Well, this structure would do the trick:

"firefox": [
  {
    "version_added": "preview"
  },
  {
    "version_added": "140",
    "flags": [
      {
        "type": "preference",
        "name": "dom.viewTransitions.enabled",
        "value_to_set": "true"
      }
    ]
  }
],

[Elchi3]

Nice, thank you, Dave! 👍