Actuatualy Firefox is not free from this menace. to recreate the problem open een Article blogpost and hit the 'close' button.
You should get a warning 'You have changes pending; are you sure you want to cancel?'
I tracked this problem down to the update.js on line #550 (and create.js) from Articles
When Articles form is initialized it does an AJAX call to get the tags for your blogpost. After getting the tags an enable() method is called to enable the tags field to be editted. BUT this enable method somehow also makes the tag_field Dirty. that's why you get the warning.
I tried to fix the problem but there is nu clean() method unfortunatly in ExtJS (https://www.sencha.com/forum/showthread.php?63445-Any-way-to-reset-the-dirty-property-of-form-fields-back-to-clean
). So i'm stuck
I don't speak ExtJS so i can't fix this problem. I hope someone else with more Extjs knowledge can fix this