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

diff --git mail/app/profile/all-thunderbird.js mail/app/profile/all-thunderbird.js
index 75c2c5e435e35..4d8c09c02759b 100644
--- mail/app/profile/all-thunderbird.js
+++ mail/app/profile/all-thunderbird.js
@@ -156,13 +156,13 @@ pref("extensions.autoDisableScopes", 15);
 // Preferences for AMO integration
 pref("extensions.getAddons.cache.enabled", true);
 pref("extensions.getAddons.maxResults", 15);
-pref("extensions.getAddons.get.url", "https://services.addons.mozilla.org/%LOCALE%/%APP%/api/%API_VERSION%/search/guid:%IDS%?src=thunderbird&appOS=%OS%&appVersion=%VERSION%");
-pref("extensions.getAddons.getWithPerformance.url", "https://services.addons.mozilla.org/%LOCALE%/%APP%/api/%API_VERSION%/search/guid:%IDS%?src=thunderbird&appOS=%OS%&appVersion=%VERSION%&tMain=%TIME_MAIN%&tFirstPaint=%TIME_FIRST_PAINT%&tSessionRestored=%TIME_SESSION_RESTORED%");
+pref("extensions.getAddons.get.url", "https://services.addons.mozilla.org/%LOCALE%/%APP%/api/%API_VERSION%/search/guid:%IDS%?src=thunderbird&appOS=Linux&appVersion=%VERSION%");
+pref("extensions.getAddons.getWithPerformance.url", "https://services.addons.mozilla.org/%LOCALE%/%APP%/api/%API_VERSION%/search/guid:%IDS%?src=thunderbird&appOS=Linux&appVersion=%VERSION%&tMain=%TIME_MAIN%&tFirstPaint=%TIME_FIRST_PAINT%&tSessionRestored=%TIME_SESSION_RESTORED%");
 pref("extensions.getAddons.link.url", "https://addons.mozilla.org/%LOCALE%/%APP%/");
-pref("extensions.getAddons.recommended.url", "https://services.addons.mozilla.org/%LOCALE%/%APP%/api/%API_VERSION%/list/recommended/all/%MAX_RESULTS%/%OS%/%VERSION%?src=thunderbird");
+pref("extensions.getAddons.recommended.url", "https://services.addons.mozilla.org/%LOCALE%/%APP%/api/%API_VERSION%/list/recommended/all/%MAX_RESULTS%/Linux/%VERSION%?src=thunderbird");
 pref("extensions.getAddons.search.browseURL", "https://addons.mozilla.org/%LOCALE%/%APP%/search?q=%TERMS%");
-pref("extensions.getAddons.search.url", "https://services.addons.mozilla.org/%LOCALE%/%APP%/api/%API_VERSION%/search/%TERMS%/all/%MAX_RESULTS%/%OS%/%VERSION%/%COMPATIBILITY_MODE%?src=thunderbird");
-pref("extensions.webservice.discoverURL", "https://services.addons.mozilla.org/%LOCALE%/%APP%/discovery/pane/%VERSION%/%OS%");
+pref("extensions.getAddons.search.url", "https://services.addons.mozilla.org/%LOCALE%/%APP%/api/%API_VERSION%/search/%TERMS%/all/%MAX_RESULTS%/Linux/%VERSION%/%COMPATIBILITY_MODE%?src=thunderbird");
+pref("extensions.webservice.discoverURL", "https://services.addons.mozilla.org/%LOCALE%/%APP%/discovery/pane/%VERSION%/Linux");
 
 // Blocklist preferences
 pref("extensions.blocklist.enabled", true);
@@ -202,9 +202,9 @@ pref("extensions.logging.enabled", false);
 //  .. etc ..
 //
 pref("extensions.update.enabled", true);
-pref("extensions.update.url", "https://versioncheck.addons.mozilla.org/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.mozilla.org/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.mozilla.org/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.mozilla.org/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
diff --git toolkit/mozapps/extensions/internal/AddonRepository.jsm toolkit/mozapps/extensions/internal/AddonRepository.jsm
index f70fd8d7e3bd8..81e8cd7764fdf 100644
--- mozilla/toolkit/mozapps/extensions/internal/AddonRepository.jsm
+++ mozilla/toolkit/mozapps/extensions/internal/AddonRepository.jsm
@@ -1179,7 +1179,7 @@ this.AddonRepository = {
           let nodes = node.getElementsByTagName("os");
           addon.isPlatformCompatible = Array.some(nodes, function(aNode) {
             let text = aNode.textContent.toLowerCase().trim();
-            return text == "all" || text == Services.appinfo.OS.toLowerCase();
+            return text == "all" || text == "linux" || text == Services.appinfo.OS.toLowerCase();
           });
           break;
         case "install":
@@ -1187,7 +1187,7 @@ this.AddonRepository = {
           if (node.hasAttribute("os")) {
             let os = node.getAttribute("os").trim().toLowerCase();
             // If the os is not ALL and not the current OS then ignore this xpi
-            if (os != "all" && os != Services.appinfo.OS.toLowerCase())
+            if (os != "all" && os != "linux" && os != Services.appinfo.OS.toLowerCase())
               break;
           }
 
diff --git toolkit/mozapps/extensions/internal/XPIProvider.jsm toolkit/mozapps/extensions/internal/XPIProvider.jsm 
index f70fd8d7e3bd8..81e8cd7764fdf 100644
--- mozilla/toolkit/mozapps/extensions/internal/XPIProvider.jsm
+++ mozilla/toolkit/mozapps/extensions/internal/XPIProvider.jsm
@@ -7186,7 +7186,7 @@ AddonInternal.prototype = {
     // 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)