FirefoxCP Isolated Web Content consuming 100% CPU & mem

[drewts86]

Steps to reproduce: Starting up Firefox. CPU and memory usage is normal before opening Firefox.

Not consuming 100% CPU & memory

Firefox is consuming 100% CPU and slowly maxing out memory usage.

Device & build information

• Device: MacBook Pro (13-inch, Mid 2012), Mac OS X 10.15 Catalina
• Build version: 140.4.0esr
• First seen version: Today is the first time seeing this.

Notes

Attachments:

Firefox 2025-10-14 13.08 profile.json.gz

┆Issue is synchronized with this Jira Task

[janbrasna]

Sorry to hear. If I'm understanding the report correctly, 140.4.0esr is not a Firefox for iOS version — you might be in the wrong place to get help. You need to either reach the desktop performance team e.g. in this https://bugzilla.mozilla.org/buglist.cgi?product=Core&component=Performance%3A%20Startup component, or there's a chat room https://wiki.mozilla.org/Matrix:Rooms#Software_Development for #perf:mozilla.org if that's more convenient — they also have some guides to make the profile as helpful as possible: https://firefox-source-docs.mozilla.org/performance/reporting_a_performance_problem.html