I've been using Themler and Firefox v41.0.1 without problems for some time.
Then I installed sliders in the header of a few templates and now when I reopen them it usually (say 9 out of 10 times) crashes Firefox just as it gets to the part where it is loading the slider.
But sometimes it works - and it seems to be SLIGHTLY more reliable if loading the template is one of the first things you do after starting Firefox.
Any idea what is going on? I have tried disabling virtually all off the add-ons and it doesn't make any real difference.