I've had NoSquint installed for some time and it's updated to version 2.1.9.1. It's been a real blessing for viewing.

However, with the past couple versions of Firefox (now version 41.0), even though I've entered exceptions for Gmail and several other sites (in NoSquint) and even though I've set NoSquint history to be retained at all times, under custom Privacy settings in Firefox it is impossible to uncheck the box for deleting NoSquint history; by that I mean I uncheck it, close the window, reopen it and find that it's still checked.

Any suggestions as to how to foil this malfunction would be gratefully received.

Nobody got a clue?!

I even scoured Firefox's config settings, and they all seem to be OK. And yet ....

I don't have Firefox installed on any of my Macs, and I have no idea what NoSquint is or does, but it stands to reason the NoSquint preferences are stored somewhere on your system. Perhaps in a plist (property list) file or even in a cookie. The old trick of moving the settings file to the desktop to force its recreation has worked for many years and might work in this case.

The trick is discovering where the settings are stored, but that should be doable with FindAnyFile or the right combination of settings in Finder's Find function.

This bug has been reported to the developer at least twice, but Jason Tackaberry says, "...I'm finding it extremely difficult to find enough time to dedicate to NoSquint..."

Thanks for that. It's been reported at least thrice; I did so (although not via GitHub) some time before posting here due to lack of response. The comments there are exactly the problems I've been experiencing.
Oh well ...

a check box not working doesn't appear on the surface to be a terribly difficult thing to troubleshoot.... I think there's something else going on here if a developer can't find time on his plate to troubleshoot a single consistent checkbox problem.