Thunderbird adds a fix for quoted styles, then its own filter throws the fix away again

'''What I see''' When I reply to an email written in classic Outlook for Windows, the quoted Outlook text gets a big gap above and below every single line, and its font changes. This happens as soon as Thunderbird processes such a message again, for example when I view my sent reply, reply to my own reply, forward it, or reopen a saved draft. Thunderbird users who receive my replies should see the same gaps. '''Why it happens (as far as I can tell)''' - Outlook writes every line as its own paragraph and relies on a small style rule that says "no extra space between paragraphs". - Since version 151, Thunderbird puts the quoted email's style rules into a protective container (`@scope`) so they cannot change my own text (bug 1967725). - Thunderbird's own safety filter for HTML emails treats this container as a suspicious rule and deletes it, together with everything inside it. The "no extra space" rule is lost, and the gaps appear. - Older versions such as Thunderbird 140 ESR don't understand the container at all and ignore the rules even in the first reply. In short: one Thunderbird feature adds the container, another Thunderbird feature removes it again. '''How to reproduce (no Outlook needed)''' The attached test message contains two quotes with the same spacing rule: quote A inside the container, quote B without it. In Thunderbird 155.0.1 quote A shows big gaps, while quote B stays tight. '''What would help''' Keep protecting my own text from the quoted styles, but in a form that Thunderbird's own filter and older email programs don't remove, for example by limiting the quoted rules to the quote with an ordinary class name instead of `@scope`. '''Technical pointers''' - Filter: pref `mail.html_sanitize.drop_conditional_css` (default true); `NoConditionalRules` in `stylesheet.rs` rejects `CssRule::Scope`. - Container: `QuoteSanitizer.sys.mjs` (Phase 2), called from `MsgComposeCommands.js`. - Tested with Thunderbird 155.0.1 on Windows 11.