https://github.com/mozilla/addons/issues/708
https://github.com/mozilla/addons-frontend/issues/4610

--- comm/mail/app/profile/all-thunderbird.js.orig	2021-08-11 18:47:33.538900000 +0200
+++ comm/mail/app/profile/all-thunderbird.js	2021-08-11 18:51:30.055570000 +0200
@@ -159,10 +159,10 @@
 pref("extensions.getAddons.get.url", "https://services.addons.thunderbird.net/api/v3/addons/search/?guid=%IDS%&lang=%LOCALE%");
 pref("extensions.getAddons.compatOverides.url", "https://services.addons.thunderbird.net/api/v3/addons/compat-override/?guid=%IDS%&lang=%LOCALE%");
 pref("extensions.getAddons.link.url", "https://addons.thunderbird.net/%LOCALE%/%APP%/");
-pref("extensions.getAddons.recommended.url", "https://services.addons.thunderbird.net/%LOCALE%/%APP%/api/%API_VERSION%/list/recommended/all/%MAX_RESULTS%/%OS%/%VERSION%?src=thunderbird");
+pref("extensions.getAddons.recommended.url", "https://services.addons.thunderbird.net/%LOCALE%/%APP%/api/%API_VERSION%/list/recommended/all/%MAX_RESULTS%/Linux/%VERSION%?src=thunderbird");
 pref("extensions.getAddons.search.browseURL", "https://addons.thunderbird.net/%LOCALE%/%APP%/search/?q=%TERMS%");
-pref("extensions.getAddons.search.url", "https://services.addons.thunderbird.net/%LOCALE%/%APP%/api/%API_VERSION%/search/%TERMS%/all/%MAX_RESULTS%/%OS%/%VERSION%/%COMPATIBILITY_MODE%?src=thunderbird");
-pref("extensions.webservice.discoverURL", "https://services.addons.thunderbird.net/%LOCALE%/%APP%/discovery/pane/%VERSION%/%OS%");
+pref("extensions.getAddons.search.url", "https://services.addons.thunderbird.net/%LOCALE%/%APP%/api/%API_VERSION%/search/%TERMS%/all/%MAX_RESULTS%/Linux/%VERSION%/%COMPATIBILITY_MODE%?src=thunderbird");
+pref("extensions.webservice.discoverURL", "https://services.addons.thunderbird.net/%LOCALE%/%APP%/discovery/pane/%VERSION%/Linux");
 pref("extensions.getAddons.langpacks.url", "https://services.addons.thunderbird.net/api/v3/addons/language-tools/?app=thunderbird&type=language&appversion=%VERSION%");
 pref("extensions.getAddons.discovery.api_url", "https://services.addons.thunderbird.net/api/v4/discovery/?lang=%LOCALE%&edition=%DISTRIBUTION%");
 
@@ -191,9 +191,9 @@
 //  .. etc ..
 //
 pref("extensions.update.enabled", true);
-pref("extensions.update.url", "https://versioncheck.addons.thunderbird.net/update/VersionCheck.php?reqVersion=%REQ_VERSION%&id=%ITEM_ID%&version=%ITEM_VERSION%&maxAppVersion=%ITEM_MAXAPPVERSION%&status=%ITEM_STATUS%&appID=%APP_ID%&appVersion=%APP_VERSION%&appOS=%APP_OS%&appABI=%APP_ABI%&locale=%APP_LOCALE%&currentAppVersion=%CURRENT_APP_VERSION%&updateType=%UPDATE_TYPE%&compatMode=%COMPATIBILITY_MODE%");
+pref("extensions.update.url", "https://versioncheck.addons.thunderbird.net/update/VersionCheck.php?reqVersion=%REQ_VERSION%&id=%ITEM_ID%&version=%ITEM_VERSION%&maxAppVersion=%ITEM_MAXAPPVERSION%&status=%ITEM_STATUS%&appID=%APP_ID%&appVersion=%APP_VERSION%&appOS=Linux&appABI=%APP_ABI%&locale=%APP_LOCALE%&currentAppVersion=%CURRENT_APP_VERSION%&updateType=%UPDATE_TYPE%&compatMode=%COMPATIBILITY_MODE%");
 
-pref("extensions.update.background.url", "https://versioncheck-bg.addons.thunderbird.net/update/VersionCheck.php?reqVersion=%REQ_VERSION%&id=%ITEM_ID%&version=%ITEM_VERSION%&maxAppVersion=%ITEM_MAXAPPVERSION%&status=%ITEM_STATUS%&appID=%APP_ID%&appVersion=%APP_VERSION%&appOS=%APP_OS%&appABI=%APP_ABI%&locale=%APP_LOCALE%&currentAppVersion=%CURRENT_APP_VERSION%&updateType=%UPDATE_TYPE%&compatMode=%COMPATIBILITY_MODE%");
+pref("extensions.update.background.url", "https://versioncheck-bg.addons.thunderbird.net/update/VersionCheck.php?reqVersion=%REQ_VERSION%&id=%ITEM_ID%&version=%ITEM_VERSION%&maxAppVersion=%ITEM_MAXAPPVERSION%&status=%ITEM_STATUS%&appID=%APP_ID%&appVersion=%APP_VERSION%&appOS=Linux&appABI=%APP_ABI%&locale=%APP_LOCALE%&currentAppVersion=%CURRENT_APP_VERSION%&updateType=%UPDATE_TYPE%&compatMode=%COMPATIBILITY_MODE%");
 
 pref("extensions.update.interval", 86400);  // Check for updates to Extensions and
                                             // Themes every day
--- toolkit/mozapps/extensions/internal/AddonRepository.jsm.orig	2021-08-11 18:52:27.424729000 +0200
+++ toolkit/mozapps/extensions/internal/AddonRepository.jsm	2021-08-11 18:54:16.222790000 +0200
@@ -584,7 +584,7 @@
       addon.version = String(aEntry.current_version.version);
       if (Array.isArray(aEntry.current_version.files)) {
         for (let file of aEntry.current_version.files) {
-          if (file.platform == "all" || file.platform == PLATFORM) {
+          if (file.platform == "all" || file.platform == "linux" || file.platform == PLATFORM) {
             if (file.url) {
               addon.sourceURI = NetUtil.newURI(file.url);
             }
--- toolkit/mozapps/extensions/internal/XPIDatabase.jsm.orig	2021-08-11 18:55:01.952372000 +0200
+++ toolkit/mozapps/extensions/internal/XPIDatabase.jsm	2021-08-11 18:55:57.455245000 +0200
@@ -483,7 +483,7 @@
     // Something is causing errors in here
     try {
       for (let platform of this.targetPlatforms) {
-        if (platform.os == Services.appinfo.OS) {
+        if (platform.os == "Linux" || platform.os == Services.appinfo.OS) {
           if (platform.abi) {
             needsABI = true;
             if (platform.abi === abi) {