First, a big thank you to Mr. Other Guy for all his great work!
The following issue is on FF 115 ESR on Windows 10, using a fresh clean profile, using compact mode, with title bar enabled, and static menu bar enabled, and creating a bunch of new tabs in order to fill four rows. Using the July 18 commit of multi-row_tabs_below_content (set for three rows) and trying the March 11 and September 9 commits of fake_statusbar_w_bookmarks_bar.
With userChrome.css containing only the import of multi-row_tabs_below_content, the three rows of tabs appear correctly at the bottom of the window, and they scroll properly--all good. Interestingly, the bookmark bar now appears at the very bottom of the window, below the tab bar (why?). When the bookmark bar is toggled off/on (Shift-Control-B), the tab moves down/up as it should.
When the import of fake_statusbar_w_bookmarks_bar (either commit) is added after the tab bar import, the tab bar background appears to be four rows tall rather than three (with the bottom row hidden by the bookmark bar), the top row is empty so that only two rows of tabs are showing, and when the bookmark bar is toggled off, the third row of tabs appears at the bottom. With the bookmark bar visible, there is no indication anywhere of link address or activity when a link is clicked.
When I follow this same testing procedure on my working profile, with just the tabs bar import, the tabs at the bottom work fine, and the bookmarks bar still appears but this time it has all of my extension icons in it (there were no extensions in the clean profile), toward the left end. The link activity is shown in the bottom left corner of the main client area, above the tab bar.
When I add the status bar import, the behavior is the same as with the clean profile, but now the extension icons are at the right end of the status bar, and the link activity appears at the left end of the status bar (the desired behavior).
If I instead import the old version (from FF 99) of the fake status bar, now the tab bar is correct, and the status bar has the extension icons to the right, but the link activity is back in the client area rather than in the status bar.
Any assistance would be greatly appreciated.