User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:89.0) Gecko/20100101 Firefox/89.0

Steps to reproduce:

Hover on persian sites tab

Actual results:

tab title moves a little

Expected results:

tab title shoudn't move

Not sure if Theme is the right place for it, but I can confirm the behavior on a Persian nightly build.

Possibly a dupe of bug 1701065

(In reply to Jared Wein [:jaws] (please needinfo? me) from comment #2)

Possibly a dupe of bug 1701065

Yeah, the behavior I'm seeing is very similar.

Please note that this issue is also reproducible on all LTR websites with RTL build.

I am not able to reproduce this anymore, so perhaps bug 1701065 did indeed fix this. Can you confirm, flod?

(In reply to Mike Conley (:mconley) (:⚙️) (Catching up on needinfos) from comment #7)

I am not able to reproduce this anymore, so perhaps bug 1701065 did indeed fix this. Can you confirm, flod?

Hm, but bug 1701065 is a dupe of this bug?
In any case, I can still reproduce this daily.

You can download the Persian build and create a new profile, it should be visible even on the default start pages.
For example, it happens on https://www.mozilla.org/en-US/privacy/firefox/

Bug 1708223 has a good example of this happening on a LTR build
https://addons.mozilla.org/en-US/firefox/addon/%D8%A7%D9%84%D8%B9%D8%B1%D8%A8%D9%8A%D8%A9-language-pack/

Same issue for me with Arabic RTL in tabs since Proton. I hope the team fixes it.

Please note that this issue could be related to 1717319

FWIW,
The problem is caused by the following css.

https://searchfox.org/mozilla-central/source/browser/themes/shared/tabs.inc.css#456-459

.tabbrowser-tab:not(:hover) > .tab-stack > .tab-content > .tab-close-button {
    padding-inline-start: 0;
    width: 17px;
}

Removing this fixes the issue.

Romain, this makes tabs pretty hard to use for our RTL users (x-ref number of duplicates). Can we prioritize this?

This seemed to not work. So by removing the rules, it doesn't prevent more of the table title from being shown. Now when the tab is hovered more is actually visible.

Going to steal this because I think given the number of dupes and how it impacts the experience of RTL users, we need to fix this.

Agreed, that makes sense to prioritize

https://hg.mozilla.org/mozilla-central/rev/9bfcfa324f1f

I was able to reproduce the issue on Win10 using Arabic build 89.0(20210524222230).
Verified as fixed on Win 10 /Ubuntu 20.4 /Mac 10.13 using Arabic build 96.0b3 (20211209163454)

Please nominate this for ESR approval when you get a chance. It grafts cleanly.

Comment on attachment 9253230 [details]
Bug 1701394 - fix tab text moving when tab label direction doesn't match UI direction, r?jaws

ESR Uplift Approval Request

• If this is not a sec:{high,crit} bug, please state case for ESR consideration: Broken tab experience for pages whose title's text direction doesn't match the browser's (LTR page titles in RTL Firefox; RTL page titles in LTR Firefox). This affects a significant minority of Firefox users.
• User impact if declined: See above
• Fix Landed on Version: 96
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Small JS/CSS-only changes that fix the jittering of the tab title only; already verified on nightly, possible fallout should be minimal / non-existent.
• String or UUID changes made by this patch: None

Comment on attachment 9253230 [details]
Bug 1701394 - fix tab text moving when tab label direction doesn't match UI direction, r?jaws

Approved for 91.5esr.

https://hg.mozilla.org/releases/mozilla-esr91/rev/de411169694a

Reproduced the issue on macOS 10.15 using an Urdu build 89.0.2 (20210622155641).
This issue is verified fixed using Firefox 91.5.0esr (20220105212146) Urdu and Arabic builds, on macOS 10.15, Ubuntu 20.04 and Windows 10 x64.