I cleared out /tmp/tl-* and $TLDIR/tl-* (where $TLDIR is my directory with the website files) and then ran a browser with export TLOPTIONS=EnableMainThread,EnableOffThread,EnableGraph export TLLOG=Default firefox -no-remote -P Test after a few seconds, I shut it down and did cp /tmp/tl* $TLDIR. The resulting tracelogger HTML view showed 4 traces to choose from: tl-data.json tl-data.16326.json, and 2 more with pids in them. When I selected tl-data.json, it popped up an error window "Failed to load http://localhost:8000/tl-data.24043.json". tl-data.24043.json does exist, but it and every other tl-*.24043.* file is zero-length except for tl-dict.24043.0.json. I assume that's why it's unhappy.