Bugzilla

**Description:**

When this feature is enabled, hovering the mouse cursor over a tab in the tab bar for 1000ms will open a detailed preview window containing the title, URL, and a screenshot of the website currently loaded in the tab being hovered. This replaces the existing tooltip behavior.

**How do we test this?**

Change the preference `browser.tabs.cardPreview.enabled` to `true`.

**When will this ship?**

We will be performing QA in the Fx124 Nightly cycle, but don't have a strict release plan so this deadline is flexible.

**Tracking bug/issue:**

**Design documents (e.g. Product Requirements Document, UI spec):** https://www.figma.com/file/cJO5SWlTCQjdOJJNtkcpUm/Tab-Hover-Preview?type=design&node-id=0-1&mode=design&t=cyu0DG6ghtzjXskg-0

**Engineering lead:** Molly Howell

**Product manager:** Ethan Piper

**The accessibility team has developed the Mozilla Accessibility Release Guidelines which outline what is needed to make user interfaces accessible:
https://wiki.mozilla.org/Accessibility/Guidelines
Please describe the accessibility guidelines you considered and what steps you've taken to address them:**

- fall back to system colors when in High Contrast Mode
- might be missing some helpful ARIA roles, but I could use some guidance on what/where (see questions below)

**Describe any areas of concern to which you want the accessibility team to give special attention:**

- how should this behave for users who aren't using a pointing device?
- should the information exposed in the preview be exposed to screen readers? Under what accessibility circumstances should we consider keeping it disabled?
- the preview is contained inside of a XUL `<panel>` element. There might be some built-in accessibility features that I'm not aware of, or other things I need to take into account here.

(moved to bug description)