How do I find the logs of Firefox? - debugging

Question

While browsing the Firefox source code, I see that a lot of logs are present. I'd like to find them on runtime to help me understand and debug something.
For example, when taking a look at nsHttpConnection.cpp, Here's what I can find :
...
LOG(("restarting transaction #%p\n", this));
mTunnelProvider = nullptr;
...
Where did the LOG lines go ? How do I find the log file containing all the logs generated by Firefox ?

Answer 1

In the case of the file nsHttpConnection.cpp, the LOG() functions are macros defined in HttpLog.h.
here's an excerpt :
#define LOG1(args) \
MOZ_LOG(mozilla::net::gHttpLog, mozilla::LogLevel::Error, args)
You can see them as shortcuts for the more complete MOZ_LOG functions.
LOG1() -> Error
LOG2() -> Warning
LOG3() -> Info
LOG() = LOG4() -> Debug
LOG5() -> Verbose
If you want to get the logs for the nsHttp module, you can set 2 environment variables, and then run firefox :
set MOZ_LOG=nsHttp:5
set MOZ_LOG_FILE=http.log
firefox
or run firefox with the command line parameters :
firefox -MOZ_LOG=nsHttp:5 -MOZ_LOG_FILE=nsHttp.log
This enables Verbose level information (and higher) and places all output in the file nsHttp.log.
The MOZ_LOG variable is composed of as <module>:level.
You can also use a more general module all to include them all.
i.e. to log all Error level informations in the file all.log:
firefox -MOZ_LOG=all:1 -MOZ_LOG_FILE=all.log
For more information on how the MOZ_LOG variable is configured, you can take a look at prlog.h