When browsing certain pages (specifically Reddit.com), going back to the previous page will refresh the whole page, which expands the comments I've collapsed and I can no longer find the comment I was looking at a moment ago. Currently I do not have any add-ons activated, but if I start Firefox in safe-mode the problem is no longer there. I have tried to refresh Firefox, but this did not solve my problem. I have also cleared my cache and this did not solve my problem either. This is a problem that seems to come and go from time to time, without any reason that I understand.