I have a lot of add ons but I disabled them by xxxing the extensions directory and then running 3.5.3.
Checked and only the java quickstart reinstalled.
Simple process for forcing the error.
Open the front page for TL with 3.5.3 and leave it open
dos deltree of the ffprofile/cache directory which will kill all but 4 or 5 files
Close firefox
immediately
Reopen firefox
Reopen
www.traderslaboratory.com
To get rid of the error. Close firefox and deltree the directory again which gets rid of all files and the directory. On rebooting firefox all is well.
Seems to work almost every time.