I accidentally added the into Firefox's built in dictionary, and since it a very common typo for me, I desperately need to delete that so it will warn me again every time I do it. I checked where Firefox stores dictionary entries, except that it doesn't seem to be the case for me. I don't have a persdict.dat file anywhere on my computer. I did a search on my entire C drive and nothing came up. Is there some new place that maybe has changed since any of those websites that I saw posted the articles about the persdict file? And to be clear, I have turned on "View Hidden Files", so it can't be that.