fix: prevent scroll jump in Firefox when expanding collapse

[mokshkimta21]

Summary

Fixes an issue where expanding a .collapse element causes a scroll jump in Firefox due to automatic focus behavior.

---

Context

• Issue: #41562
• Firefox shifts focus to the collapsing element when tabindex="-1" is used, causing the page to scroll unexpectedly.
• This behavior is specific to Firefox and does not affect Chrome or Safari.

---

Changes

• Detects Firefox using the user agent.
• Prevents focusing the collapse element in Firefox to avoid scroll jumps.
• Keeps current behavior unchanged for other browsers.

---

Before & After

Browser	Scroll Jump Before	Scroll Jump After
Firefox	Yes	No
Chrome	No	No
Safari	No	No

---

Testing

• Verified fix on:
  • Firefox 128 (macOS)
  • Chrome 115
  • Safari 17
• Ran npm run dist to generate updated files.

---

Checklist

• Follows Bootstrap's code style and conventions.
• Only affects Firefox behavior.
• Fix confirmed on live test.
• Addresses the root issue (Extended margin and padding #41562).
• Does not introduce any regressions.

[julien-deramond]

Thanks for creating a PR @mokshkimta21
Quick feedback without having tested the branch so far:

• The reference of the issue in the description is not the right one. This fix is not linked to Extended margin and padding #41562. Please update the reference in the description.
• Please don't use emojis in comments.
• Please don't commit the js/dist files.
• Please add some unit tests.

[mdo]

v6 addresses the focus-restore scroll family with {preventScroll} (see #42544). Closing as superseded — please open a new issue if the Firefox collapse scroll-jump still reproduces on v6-dev.