I found that you can run Firefox in debug mode by using the flag -g but it doesnt really show anything interesting:
firefox -g
MOZILLA_FIVE_HOME=/usr/lib64/firefox
LD_LIBRARY_PATH=/usr/lib64/firefox:/usr/lib64/firefox/plugins:/usr/lib64/firefox
DISPLAY=:0.0
FONTCONFIG_PATH=/etc/fonts:/usr/lib64/firefox/res/Xft
DYLD_LIBRARY_PATH=/usr/lib64/firefox:/usr/lib64/firefox
LIBRARY_PATH=
SHLIB_PATH=/usr/lib64/firefox:/usr/lib64/firefox
LIBPATH=/usr/lib64/firefox:/usr/lib64/firefox
ADDON_PATH=
MOZ_PROGRAM=/usr/lib64/firefox/firefox
MOZ_TOOLKIT=
moz_debug=1
moz_debugger=
moz_debugger_args=
/usr/lib64/firefox/run-mozilla.sh: line 84: type: ddd: not found <------ Of any relevance?
/usr/bin/gdb --args /usr/lib64/firefox/firefox
GNU gdb (GDB) Red Hat Enterprise Linux (7.2-92.el6)
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <
http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law. Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<
http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/lib64/firefox/firefox...(no debugging symbols found)...done.
Missing separate debuginfos, use: debuginfo-install firefox-52.4.0-1.el6.centos.x86_64
(gdb) run
Starting program: /usr/lib64/firefox/firefox
[Thread debugging using libthread_db enabled]
[New Thread 0x7fffed80b700 (LWP 7034)]
[Thread 0x7fffed80b700 (LWP 7034) exited]
Detaching after fork from child process 7035.
[New Thread 0x7fffed80b700 (LWP 7039)]
[New Thread 0x7fffe9dff700 (LWP 7040)]
[New Thread 0x7fffe93fe700 (LWP 7041)]
[New Thread 0x7fffe89fd700 (LWP 7042)]
[New Thread 0x7fffe7dff700 (LWP 7043)]
[New Thread 0x7fffe73fe700 (LWP 7044)]
[New Thread 0x7fffe69fd700 (LWP 7045)]
[New Thread 0x7fffe5ffc700 (LWP 7046)]
[New Thread 0x7fffe55fb700 (LWP 7047)]
[New Thread 0x7fffe4bfa700 (LWP 7048)]
[New Thread 0x7fffe41f9700 (LWP 7049)]
[New Thread 0x7fffe37f8700 (LWP 7050)]
[New Thread 0x7fffe2df7700 (LWP 7051)]
[New Thread 0x7fffe1dff700 (LWP 7052)]
[New Thread 0x7fffe13fe700 (LWP 7053)]
It just hangs here and doesn't go any further.