Split out disabling Firefox Home (Activity Stream) to use in base-browser

Merge Info

• Related Issues

  • #41609 (closed)
  • #31575 (closed)
  • https://gitlab.torproject.org/tpo/applications/privacy-browser/-/issues/39

• Backport Timeline

  • Immediate - patchsets for critical bug fixes or other major blocker (e.g. fixes for a 0-day exploit) OR patchsets with trivial changes which do not need testing (e.g. fixes for typos or fixes easily verified in a local developer build)
  • Next Minor Stable Release - patchset that needs to be verified in nightly before backport
  • Eventually - patchset that needs to be verified in alpha before backport
  • No Backport - patchset for the next major stable

• Upstream Merging

  • Don't merge to base-browser. Instead, we can cherry pick two of the commits that are meant to be in base-browser in a separate MR.

• Issue Tracking

  • tor-browser-build#40724 (closed)

Change Description

We split out the disabling of Firefox Home (Activity Stream) from "Bug 10760: Integrate TorButton to TorBrowser core" commit and create a separate commit for base-browser that applies the same change, but using "about:blank" instead of "about:tor". Specifically, as commits:

1. Revert the part of "Bug 10760: Integrate TorButton to TorBrowser core" related to Firefox Home.
2. Fixup "Firefox preference override" from base-browser since we want the newtab preference to be part of our new commit instead.
3. A new commit that disable Firefox Home. The home page is either a URL or "about:blank", and the new tab can only be "about:blank". We attach this commit to #31575 (closed) since that roughly corresponds to disabling Activity Stream.
4. Fixup "Bug 10760: Integrate TorButton to TorBrowser core" to make "about:tor" the default home page, and available as a page for new tab.
5. Reword "Bug 10760: Integrate TorButton to TorBrowser core" to remove the mention of #31575 (closed).