User Agent Mozilla/5.0 (Windows NT 6.1; WOW64; rv:55.0) Gecko/20100101 Firefox/55.0 I have a problem with Firefox Beta 53. It also happens in Nightly 55. Doesn't happen in Beta 52, ESR 45. Sometimes I need to change theme in devtools to 'light' if some of the usability issues become more noticeable. After changing devtools theme, tab strip scrolls to the beginning, so current scroll position is lost. Here's how to reproduce the bug: 1. Pin tab 2. Scroll tab strip to the end 3. In the pinned tab open devtools and change theme in devtools from dark to light Result: Tab strip is scrolled to the beginning Expected: No movement in tab strip

WFM in Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:58.0) Gecko/20100101 Firefox/58.0 ID:20171007220156.

This is a bug about the browser tabs, not the devtools toolbox tabs. Furthermore, since FF57, the dark/light themes are changed within the browser customization screen, not within devtools. Switching devtools to dark doesn't change the browser to dark. Finally, I tried reproducing with both the STR provided and with changing to the dark theme in the customization screen and I did not have the problem. So I'll close the bug for now. Please feel free to re-open if I got it wrong.