Please Refresh but do this 1st: *https://support.mozilla.org/en-US/kb/export-firefox-bookmarks-to-backup-or-transfer *https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles then *https://support.mozilla.org/en-US/kb/refresh-firefox-reset-add-ons-and-settings TEST....... If no issues then Extensions which need to be added back in 1 at a time and tested ..... Or it is your Profile : Make a new one and test ...: *https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles If is your Profile : *https://support.mozilla.org/en-US/kb/recovering-important-data-from-an-old-profile *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox Note: Any customization will revert back to default, you will also need to reinstall Extensions. Please let us know if this solved your issue or if need further assistance.

See also: *https://developer.mozilla.org/en-US/docs/Web/HTML/Element/input/number

As suspected, I am now 99% sure that the problem is with bad source code. I inspected and tweaked the source code on a web site and the problem went away! I have now reopened my support ticket with the developer and have provided them with the information to (hopefully) fix this issue and prove to them that, as I originally told them "I'm right, you're wrong." Thanks for the help and attention, I'll take it from here!

That was good work. Well done.