BiDI Mail UI: Improved Right-to-Left language support for Thunderbird

_{(See it also on addons.thunderbird.net)}

The problem

So, you use the Thunderbird mail client, and you send or receive email in a right-to-left (RTL) language, such as Arabic, Farsi or Hebrew. Thunderbird is based on Mozilla/Firefox, and Firefox supports webpages in those languages, right? So, surely Thunderbird must have bidirectional capabilities and support, right? Wrong :-(

The text emails you receive are always rendered in left-to-right (LTR) direction, regardless of their langauge
... and so are the HTML messages, if they don't have explicit direction settings
When you compose messages, it's the same thing: The composition window assumes you're writing LTR content only.
And let's not even talk about setting directions on a paragraph-by-paragraph level! None of that.
Sometimes, you receive emails with Arabic/Farsi/Hebrew content, which show up as gibberish, because Thunderbird didn't correctly determine their character set encoding - and you have to set it manually.
... and if you have a message with text in more than one character set encoding, you're out of luck, because you can only choose exactly one encoding for the whole message.

This has been the case for over 25 years (!)... although there is an idea for potential crowdfunding of work on changing this situation, which is worth checking out. In the mean time - BiDi Mail UI is the (imperfect) solution to your problems!

Key features

BiDi Mail UI extension adds functionality both for reading and composing e-mail (and news/NNTP) messages.

Reading:

Detects mis-decoded messages in common RTL languages (and corrects the decoding if Thunderbird allows it)
Decodes RTL text in mixed-character-set messages (UTF-8 and windows-1255/6)
Detects and applies intended direction of mail messages
Detects and applies intended directions of individual paragraphs within a mail message

Composition:

Allows setting the direction of the entire message
Allows setting the direction of individual paragraphs (in HTML mail)
Allows insertion of LRM/RLM marks, using Ctrl+Shift+L/Ctrl+Shift+R or the context menu

The extension in action

This screenshot was taken with Thunderbird 68.8.0 on Devuan GNU/Linux Beowulf, with BiDi Mail UI 0.10. Note: The message in the background of the composition window is a plain text message; its paragraph directions were set automatically by the extension.

Origins of the extension

BiDi Mail UI was originally based on an old extension by Moofie, called HebMailPack; it was developed in order to fix Mozilla's Bug 119857. Eventually, it was completely rewritten, with much functionality added and improved.

For a long while, the extension was developed and maintained by Eyal Rozenberg and Asaf Romano on MozDev; Asaf eventually retired from maintenance, and several years later, MozDev wound down. Eyal, the current maintainer, migrated the extension to GitHub.

See also the Credits page on the repository wiki.

Bugs, suggestions, feedback, etc.

Read the FAQ section of the wiki; your answer is probably in there. If it isn't, please search the issues page of this repository, to check if it's already been reported. not, file a new issue.