Mozilla Firefox

Where Mozilla Firefox keeps its logs

Mozilla Firefox logs to %APPDATA%\Mozilla\Firefox\Crash Reports\ on Windows. 1 other Windows log location is recorded below, including paths for Microsoft Store (MSIX). These paths were verified for exe, msi and msix installs - a different installer, or a portable copy, can put them somewhere else.

Mozilla Firefox logs to ~/Library/Application Support/Firefox/Crash Reports/ on macOS. These paths were verified for dmg and pkg installs - a different installer, or a portable copy, can put them somewhere else.

Mozilla Firefox logs to ~/.mozilla/firefox/Crash Reports/ on Linux. 2 other Linux log locations are recorded below, including paths for Snap and Flatpak. These paths were verified for deb, snap and flatpak installs - a different installer, or a portable copy, can put them somewhere else.

Paths are printed exactly as Mozilla Firefox writes them. Environment variables like %LOCALAPPDATA% and $XDG_STATE_HOME are never expanded, so a path can be pasted straight into a shell. Where a path differs between installer types or shipping flavours, each one is racked as its own card below - why that happens.

Finding your way around Windows, macOS and Linux.

How to turn on debug logging for Mozilla Firefox

1. Open about:logging in Firefox.
2. Pick a preset (for example networking or cookies) or enter the modules to log.
3. Choose whether to log to a file or to the Firefox Profiler, then start logging.
4. Windows: Alternatively, in a command prompt run set MOZ_LOG=timestamp,rotate:200,nsHttp:5,cache2:5,nsSocketTransport:5,nsHostResolver:5.
5. Windows: Run set MOZ_LOG_FILE=%TEMP%\log.txt.
6. macOS and Linux: Alternatively, in a terminal run export MOZ_LOG=timestamp,rotate:200,nsHttp:5,cache2:5,nsSocketTransport:5,nsHostResolver:5.
7. macOS and Linux: Run export MOZ_LOG_FILE=/tmp/log.txt.
8. Start Firefox from that same prompt or terminal.
9. Levels run from 1 (Error) to 5 (Verbose); rotate:N caps the log at N MB across rotating files.

How to collect Mozilla Firefox logs

1. Collect every log file from the log folder; Firefox writes one file per process, named with the process type and PID.
2. Windows and macOS: Sandboxed content processes cannot write log files, so log to the Firefox Profiler from about:logging instead.
3. If you logged to the Firefox Profiler, upload the profile and share the link.
4. For crashes, open about:crashes and copy the crash IDs.