The sordid details are in this post in Susan’s thread about Firefox’s latest security updates.
THIS thread is so that her thread doesn’t get hijacked by any discussion pertaining to this specific problem, as I’d like to get feedback from others who may also have this problem.
UPDATE: After testing involving a brand new out of the box portable version of Firefox 138, I was able to reproduce this behavior consistently. I “installed” a portable version of Firefox 138 in its own dedicated directory and launched it, which brought up all of the screens you see the very first time you use Firefox these days.
Without modifying ANY of the default settings that come “right out of the box”, I immediately went to the privacy and security section of the settings and selected “Custom”, then immediately went to about:config and set the setting that reveals a link that will allow you to set what level of tracking content blocking you want in Firefox (see the first image in the post linked to above). I then refreshed the privacy and security settings page, and the link showed up. Upon clicking the link, a nearly blank box showed up which was identical to the one shown in the second image in the post linked to above.
To me, the above behavior very strongly suggests the behavior is all within Firefox 138 and is a bug. If the behavior were a result of something in my profile, then it wouldn’t have happened on the “right out of the box” installation of Firefox 138 portable.
Suggestions, ideas? At this point I’m wondering just how I can report this on Bugzilla, the bug report pages for Firefox and Thunderbird.
