Bug 42443: Shrink window to match letterboxing size when the emtpy area is clicked.

Merge Info

Related Issues

• #42443 (closed)

Backporting

Timeline

• Immediate: patchset needed as soon as possible
• 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 (preferred): patchset for the next major stable

(Optional) Justification

• Emergency security update: patchset fixes CVEs, 0-days, etc
• Censorship event: patchset enables censorship circumvention
• Critical bug-fix: patchset fixes a bug in core-functionality
• Consistency: patchset which would make development easier if it were in both the alpha and release branches; developer tools, build system changes, etc
• Sponsor required: patchset required for sponsor
• Localization: typos and other localization changes that should be also in the release branch
• Other: please explain

Merging

• Merge to tor-browser - !fixups to tor-browser-specific commits, new features, security backports
• Merge to base-browser - !fixups to base-browser-specific commits, new features to be shared with mullvad-browser, and security backports
  • NOTE: if your changeset includes patches to both base-browser and tor-browser please clearly label in the change description which commits should be cherry-picked to base-browser after merging

Issue Tracking

• Link resolved issues with appropriate Release Prep issue for changelog generation

Review

Request Reviewer

• Request review from an applications developer depending on modified system:
  • NOTE: if the MR modifies multiple areas, please /cc all the relevant reviewers (since gitlab only allows 1 reviewer)
  • accessibility : henry
  • android : clairehurst, dan
  • build system : boklm
  • extensions : ma1
  • firefox internals (XUL/JS/XPCOM) : ma1
  • fonts : pierov
  • frontend (implementation) : henry
  • frontend (review) : donuts, richard
  • localization : henry, pierov
  • macos : clairehurst, dan
  • nightly builds : boklm
  • rebases/release-prep : dan, ma1, pierov, richard
  • security : ma1
  • signing : boklm, richard
  • updater : pierov
  • misc/other : pierov, richard

Change Description

How Tested

Resize a window so that some letterboxing margin appears, then double click the margin to shrink the outer window back to fit the rounded content area with no margin. Try with different size and also extra browser chrome (notification bars, dev tools, side panel...)

toolkit/components/resistfingerprinting/RFPHelper.sys.mjs

@@ -750,8 +750,27 @@ class _RFPHelper {
     });
   }
 
+  // We will attach this method to each browser window. When called
+  // it will instantly resize the window to exactly fit the selected
+  // (possibly letterboxed) browser.
+  shrinkToLetterbox() {
+    let { selectedBrowser } = this.gBrowser;
+    let stack = selectedBrowser.closest(".browserStack");
+    const outer = stack.getBoundingClientRect();
+    const inner = selectedBrowser.getBoundingClientRect();
+    this.resizeBy(inner.width - outer.width, inner.height - outer.height);
+  }
+
+  _onWindowDoubleClick(e) {
+    if (e.target.classList.contains("browserStack")) {
+      e.currentTarget.shrinkToLetterbox();
+    }
+  }
+
   _attachWindow(aWindow) {
     aWindow.addEventListener("sizemodechange", windowResizeHandler);
+    aWindow.shrinkToLetterbox = this.shrinkToLetterbox;
+    aWindow.addEventListener("dblclick", this._onWindowDoubleClick);
     aWindow.gBrowser.addTabsProgressListener(this);
     aWindow.addEventListener("TabOpen", this);
     const resizeObserver = (aWindow._rfpResizeObserver =
@@ -783,9 +802,12 @@ class _RFPHelper {
       let browser = tab.linkedBrowser;
       this._resetContentSize(browser);
     }
+    aWindow.removeEventListener("dblclick", this._onWindowDoubleClick);
+    delete aWindow.shrinkToLetterbox;
     aWindow.removeEventListener("sizemodechange", windowResizeHandler);
   }
 
+
   _handleDOMWindowOpened(win) {
     let self = this;