[Reconciler] Fix: "Should not already be working" in Firefox after a breakpoint/alert #17355

[prashant3030223]

Summary

This PR addresses the "Should not already be working" invariant error that occurs in Firefox when an alert() or debugger breakpoint is triggered. In these scenarios, the browser flushes the task queue while a React render/commit is already in progress. By adding getExecutionContext() guards to the scheduler's entry points, we ensure that re-entrant work is correctly deferred until the current work loop completes.

Fixes #17355

How did you test this change?

I verified the change by analyzing the execution context flow and ensuring the guards correctly identify the RenderContext and CommitContext during re-entrant calls. This pattern is consistent with existing fixes for Safari's microtask flushing behavior in ReactFiberRootScheduler.js.
I also manually verified that the getExecutionContext() bitmask correctly identifies active work phases, preventing the performWorkOnRoot from throwing when called re-entrantly.

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[wyattloveslife-create]

Hey thats not how this works I'm just in one of my old phones that holds these accounts. Please be nice

…

On Sun, May 3, 2026 at 2:00 AM Prashant Yadav ***@***.***> wrote: Summary This PR addresses the "Should not already be working" invariant error that occurs in Firefox when an alert() or debugger breakpoint is triggered. In these scenarios, the browser flushes the task queue while a React render/commit is already in progress. By adding getExecutionContext() guards to the scheduler's entry points, we ensure that re-entrant work is correctly deferred until the current work loop completes. Fixes #17355 <#17355> How did you test this change? I verified the change by analyzing the execution context flow and ensuring the guards correctly identify the RenderContext and CommitContext during re-entrant calls. This pattern is consistent with existing fixes for Safari's microtask flushing behavior in ReactFiberRootScheduler.js. I also manually verified that the getExecutionContext() bitmask correctly identifies active work phases, preventing the performWorkOnRoot from throwing when called re-entrantly. ------------------------------ You can view, comment on, or merge this pull request online at: #36403 Commit Summary - 88e0849 <88e0849> Fix: avoid re-entrant work during render or commit File Changes (1 file <https://github.com/facebook/react/pull/36403/files>) - *M* packages/react-reconciler/src/ReactFiberRootScheduler.js <https://github.com/facebook/react/pull/36403/files#diff-b3d2d7db3b8f8517d9b1868d74049fadd238467c0a85f7f28d81a85db1f587da> (12) Patch Links: - https://github.com/facebook/react/pull/36403.patch - https://github.com/facebook/react/pull/36403.diff — Reply to this email directly, view it on GitHub <#36403>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/BZ75UJ2WBM4SU324XAYV3IL4Y4DDLAVCNFSM6AAAAACYO4KXH6VHI2DSMVQWIX3LMV43ASLTON2WKOZUGM3TCMZSGU2DEMA> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>