User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:89.0) Gecko/20100101 Firefox/89.0

Steps to reproduce:

1. Set document title to a very long string that starts with a right-to-left mark, e.g. document.title = "\u200fabcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".
2. Hover the tab in the tab list at the top of the window.

Actual results:

The trimmed tab document title moves slightly to the left in the tab card.

Expected results:

The document title should not move when hovered.

Hi Rummskartoffel!
I was not able to reproduce this issue on latest Nightly version 91.0a1 (2021-06-22)(64-bit) on Windows 10. Could you please add some screen recording showing us the problem? It might help us to reproduce it.
Also, please try to reproduce it on latest Nightly and tell us your input. You can download it from here: https://www.mozilla.org/en-US/firefox/nightly/all/.
Thanks!

The bug also occurs on Nightly 91.0a1 (2021-06-21) (64-bit) for me. It's demonstrated in the video I attached. Setting the title as I described in my initial report is the only prerequisite for triggering it.

Thank you for your reply. I was able to reproduce it follow the next steps:

• Launch Firefox
• Open Console
• Write "document.title = "\u200fabcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
• Hover over Tab title

Actual result: Tab title moves to the left

Regression range:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=f63b119397f3fbef01734701fdd8c2224d2f7dd8&tochange=8aa1b80a8c6b66cccc2e37080fbf6197eee8d801

I'll change flags accordingly. Severity suggested S3.

Note: Could be duplicated by 1701394

(In reply to Marcela from comment #3)

Regression range:
https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=f63b119397f3fbef01734701fdd8c2224d2f7dd8&tochange=8aa1b80a8c6b66cccc2e37080fbf6197eee8d801

That can't be it, unfortunately. Can you take another attempt at mozregression?

Nevermind, the other bug has a regression range already.

Dao, should we mark this one as dup of bug 1701394?