Firefox about:memory shows unexplained memory growth – is it a leak?

Diagnosing Memory Growth in Firefox

The goal is to determine whether a rising memory footprint reported by about:memory and about:processes represents a genuine leak or normal caching behavior. Firefox’s multi‑process architecture isolates sites into separate content processes, so a single content process that grows without bound often signals a site‑level leak. Extensions can also trigger persistent memory usage, but their impact is only visible when they are enabled. The key uncertainty is distinguishing unbounded memory growth from legitimate caching that Firefox will release under pressure.

To make this decision, one must compare memory usage before and after a reproducible workload, observe whether a “Minimize memory usage” operation reclaims the excess, and verify that the growth persists when running in Troubleshoot Mode (extensions disabled). The challenge is that normal caching can appear as growth until the system triggers reclamation, which may not happen in a test session.

What metrics or patterns in the about:memory report most reliably indicate a true leak? Is a single content process whose memory never drops after a repeatable workload sufficient evidence to file a bug? How can we confirm that the observed growth is not just a cache that would be freed under system pressure?