Thanks for posting, silversurfer.Firefox 143.0.3 official release later today. Note: including security fixes
https://www.firefox.com/en-US/firefox/143.0.3/releasenotes/
The Firefox 143.0.3 release notes mention:
"Adjusted the timing of the new drag-to-pin interaction cue for better reliability. (Bug 1989344)"
Firefox 143.0 introduced "Tabs can now be pinned by dragging them to the start of the tab strip," and that feature has been annyoing me ever since.
Firefox 143.0.3 introduces the about:config preference browser.tabs.dragDrop.pinInteractionCue.delayMS
Changing the value of this preference to 1200-1500 is equivalent to turning off the drag-to-pin feature.
Source, Mozilla Connect post by asafko.

