fix: memory leak from detached snap iframes

[ocnc]

Note

Addresses memory leaks in snap execution lifecycle.

• In IframeExecutionService.terminateJob, cast to HTMLIFrameElement, navigate to about:blank, then remove the iframe to ensure the prior document unloads (notably for Firefox)
• In BaseSnapExecutor.onTerminate, remove unhandledrejection and error listeners if registered and clear handler refs to enable garbage collection

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This fix should address:

MetaMask/metamask-extension#38847
MetaMask/metamask-extension#34428
MetaMask/metamask-extension#35567

My profiler showed a firefox extension (Metamask) hogging > 10GB of RAM, and the digging lead to finding event listeners aren't cleaned up on termination

[Jeko83]

looks good to me

[FrederikBolding]

Do you have a way to reproduce/prove this? When I tested locally, about:memory did not show any references to Snaps iframes after they were removed.

[ocnc]

Hi, thanks for getting to this:

Reproduction environment:

Firefox 146.0.1
MacOS 26.2

Steps for reproduction:

1. Completely quit firefox & reopen to a fresh window
2. Unlock metamask, close extension window
3. about:memory -> GC
4. Open a tab, navigate to app.aave.com (i think any dapp works). Connect wallet (disconnect if already connected)
5. Wait a minute
6. about:memory -> GC -> Measure & Save a memory report
7. Wait another few minutes
8. about:memory -> GC -> Measure & Save a memory report

Evidence of Memory Leak

Controlled Test (Firefox)

Fresh browser profile, measured with about:memory after forcing GC:

Time	Action	Active	Detached	Leaked
0:00	Fresh unlock	0	0	0 MB
+1 min	Connect to dapp	5	1	~7 MB
+5 min	Waiting around	3	8	~47 MB
+7 min	Final measurement	4	12	~68 MB

Result: 68 MB leaked in 7 minutes of normal usage

What's happening

1. Snaps create iframes at execution.metamask.io
2. When terminated, iframe.remove() is called
3. But event listeners keep references → iframes stay in memory
4. Firefox reports them as top(none)/detached/ (removed from DOM, still in memory)