See attached, the highlighted icon should be reversed for RTL.

Adding this code:

#toolbox-meatball-menu-dock-window:-moz-locale-dir(rtl) .label::before {
  transform: scaleX(-1);
}

somewhere around here:
https://searchfox.org/mozilla-central/source/devtools/client/themes/toolbox.css#246
... seems to fix it for me.

Thanks for filing. I'd definitely take a patch if someone is interested in fixing it. This might be a good first bug for someone wanting to try their first contribution on the mozilla source code.
The change is in devtools as shown in comment 0. The docs to contribute to devtools can be found here: http://docs.firefox-dev.tools/

hi, I am really excited to work on my very first bug. Is it open??

Hi Vishal, yes this bug is still open and available for you to pick up if you want to.
I'll assign it to you now. Let me know if you need anything. I suggest going through the docs I mentioned in comment 1 to learn how to get the code, build firefox and test your changes. Once you've done that, the docs also mention how to post the code changes up for review.
Happy coding!

Finding difficulty in cloning the repository.

it is showing error in teminal during clonong

vishal@vishal-HP-Notebook:~/fr$ hg clone https://hg.mozilla.org/mozilla-central
destination directory: mozilla-central
applying clone bundle from https://hg.cdn.mozilla.net/mozilla-central/1e3244e602fc0373508049b6fe544332f800f033.zstd-max.hg
error fetching bundle: [Errno 110] Connection timed out
abort: error applying bundle
(if this error persists, consider contacting the server operator or disable clone bundles via "--config ui.clonebundles=false")

Please, help me to get out of the problem mentioned in comment 4..

I tried hard to build and run firefox locally but it is not working. Please help me.

Hi Vishal. It looks like the clone took too long and mercurial just timed out. It's likely a network issue.
Helping on bugzilla will be a bit hard though due to its asynchronous nature. I would suggest joining the Mozilla IRC and in particular the #introduction channel and report the problem there. There are many people monitoring this channel and they will either be able to help you directly or point you to the right place for asking. IRC will be a better option given that people will be able to ask and answer questions quickly.

Before the icon was reverse for rtl . But now it is in correct form.

hi, I submitted the patch..
Would you please review it??

(In reply to Vishal Singh from comment #9)

hi, I submitted the patch..
Would you please review it??

I think you should have added :pbro as a reviewer to the patch in phabricator.

Before the icon was reverse for rtl . But now it is in correct form.

Reviewed and landed in phabricator. Thank you!

https://hg.mozilla.org/mozilla-central/rev/3f4a4ab9eed0