release(runway): cherry-pick fix: Fix Firefox detatched-window memory leak by avoiding DocumentPictureInPicture instantiation in Snow hook cp-13.39.2 - #44401
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… leak by avoiding `DocumentPictureInPicture` instantiation in Snow hook cp-13.39.2 (#44352) ## **Motivation** On Firefox, every closed MetaMask window (popup, notification, home) is retained in memory ([#42891](#42891) and recent internal reports). - **Rate:** ~70 detached window entries (~105MB, fresh test wallet) per popup open/close, linear with use. 30 cycles leave **3.56GB** (13.37.0) / **3.31GB** (13.38.1) of detached documents, surviving forced GC. State-heavy wallets multiply every retained document. - **Mechanism** (heap-graph traced, intervention-tested): Snow's picture-in-picture hook reads `win?.documentPictureInPicture?.requestWindow` in every window. The read lazily instantiates a per-window `DocumentPictureInPicture`, and Firefox's cycle collector fails to break the instance's preserved-wrapper cycle after window close, pinning the entire realm. - **Why now:** Firefox shipped the API in 151 (May 2026). The April-2023 hook was dormant until users auto-updated. The collection failure itself is a Gecko defect (upstream filing in progress; prior art: [Bugzilla 1902438](https://bugzilla.mozilla.org/show_bug.cgi?id=1902438)), but this fix does not depend on Mozilla. ## **Description** Applies the upstream Snow fix ([LavaMoat/snow#171](LavaMoat/snow#171)) as a Yarn patch: the hook moves from the per-window instance to `DocumentPictureInPicture.prototype`, reached through the interface object, which does not invoke the instance-creating getter. - Call semantics unchanged: instance lookup falls through to the patched prototype, `this` stays the instance, same wrapped native. Snow's PiP realm monitoring is preserved. - The patch covers `snow.prod.js` and `snow.js` in addition to `src/request.js`: the extension consumes Snow's prebuilt bundle as a LavaMoat static shim (`LavamoatPlugin`), and webpack never processes `@lavamoat/snow/**`. - **Interim:** remove this patch when `@lavamoat/snow` is bumped to a release containing the upstream fix. The bump is the removal trigger. ## **Cherry-pick candidacy** - Affected population: every Firefox user on 151+ (effectively the whole Firefox base via auto-update). Reproduces from a fresh wallet in five popup opens. No workaround short of a browser restart. - Proposed: next RC, with a hotfix on the current production line worth considering. - Snow is security-team-owned. Their sign-off on shipping a patched Snow is part of this review. ## **Verification** | Check | Result | |---|---| | Intervention: official 13.37.0 artifact, only this hook changed, 30 cycles | **+2,100 docs (3.35GB) → -13 (1.6MB total)**. Hook is the sole delta, so this is also the causal proof | | This PR's CI artifact (`d4dd55f`), probed directly | Patched hook present; 5 cycles: +7 KB-scale entries (1.1MB) vs +345 docs (+534MB) stock | | Field | Original reporter confirms the leak is gone on this PR's CI build | | Independent repro | Manual steps + automated probe: https://github.com/MajorLift/snow/tree/verification/pip-realm-leak/verification | ## **Related issues** Fixes: #42891 ## **Manual testing steps** 1. Install this PR's Firefox build (metamaskbot comment) in a fresh profile via `about:debugging` → Load Temporary Add-on. Onboard with a test SRP. 2. Confirm the fix is live: extension console → `DocumentPictureInPicture.prototype.requestWindow.name` → `"open"` (stock: `"requestWindow"`). 3. Open/close the popup five times, visiting activity or a swap view on a few opens. 4. `about:memory` → Minimize memory usage → Measure → filter `detached`: no `moz-extension` UI-document cohorts (stock: ~70 entries / ~105MB per cycle). ## **Screenshots/Recordings** Heap-graph traces, memory reports, and retaining-path analysis: see the verification bundle above. ## **Pre-merge author checklist** - [x] I've followed [MetaMask Contributor Docs](https://github.com/MetaMask/contributor-docs) and [MetaMask Extension Coding Standards](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/CODING_GUIDELINES.md). - [x] I've completed the PR template to the best of my ability - [x] I've included tests if applicable - [x] I've documented my code using [JSDoc](https://jsdoc.app/) format if applicable - [x] I've applied the right labels on the PR (see [labeling guidelines](https://github.com/MetaMask/metamask-extension/blob/main/.github/guidelines/LABELING_GUIDELINES.md)). Not required for external contributors. CHANGELOG entry: Fixed a memory leak on Firefox where closed MetaMask windows were retained in memory, growing extension memory use with every popup open
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⚡ Performance Benchmarks (Total: 🟢 12 pass · 🟡 11 warn · 🔴 1 fail)
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DocumentPictureInPictureinstantiation in Snow hook cp-13.39.2 (fix: Fix Firefox detatched-window memory leak by avoidingDocumentPictureInPictureinstantiation in Snow hook cp-13.39.2 #44352)Motivation
On Firefox, every closed MetaMask window (popup, notification, home) is
retained in memory
(#42891
and recent internal reports).
popup open/close, linear with use. 30 cycles leave 3.56GB (13.37.0)
/ 3.31GB (13.38.1) of detached documents, surviving forced GC.
State-heavy wallets multiply every retained document.
picture-in-picture hook reads
win?.documentPictureInPicture?.requestWindowin every window. The readlazily instantiates a per-window
DocumentPictureInPicture, andFirefox's cycle collector fails to break the instance's
preserved-wrapper cycle after window close, pinning the entire realm.
hook was dormant until users auto-updated. The collection failure itself
is a Gecko defect (upstream filing in progress; prior art: Bugzilla
1902438), but
this fix does not depend on Mozilla.
Description
Applies the upstream Snow fix
(LavaMoat/snow#171) as a
Yarn patch: the hook moves from the per-window instance to
DocumentPictureInPicture.prototype, reached through the interfaceobject, which does not invoke the instance-creating getter.
prototype,
thisstays the instance, same wrapped native. Snow's PiPrealm monitoring is preserved.
snow.prod.jsandsnow.jsin addition tosrc/request.js: the extension consumes Snow's prebuilt bundle as aLavaMoat static shim (
LavamoatPlugin), and webpack never processes@lavamoat/snow/**.@lavamoat/snowis bumped to arelease containing the upstream fix. The bump is the removal trigger.
Cherry-pick candidacy
Firefox base via auto-update). Reproduces from a fresh wallet in five
popup opens. No workaround short of a browser restart.
considering.
is part of this review.
Verification
d4dd55f), probed directly|
Related issues
Fixes: #42891
Manual testing steps
profile via
about:debugging→ Load Temporary Add-on. Onboard with atest SRP.
DocumentPictureInPicture.prototype.requestWindow.name→"open"(stock:
"requestWindow").a few opens.
about:memory→ Minimize memory usage → Measure → filterdetached:no
moz-extensionUI-document cohorts (stock: ~70 entries / ~105MB percycle).
Screenshots/Recordings
Heap-graph traces, memory reports, and retaining-path analysis: see the
verification bundle above.
Pre-merge author checklist
Docs and MetaMask
Extension Coding
Standards.
if applicable
guidelines).
Not required for external contributors.
CHANGELOG entry: Fixed a memory leak on Firefox where closed MetaMask
windows were retained in memory, growing extension memory use with every
popup open 942441b