Bug 42438: Tweaks to the migration wizard.

Remove the items not compatible with our features (such as history) from
the migration wizard.

On Linux, allow to specify an alternative home directory, since we
usually change $HOME in our startup script.

browser/components/migration/ChromeMigrationUtils.sys.mjs

@@ -342,6 +342,8 @@ export var ChromeMigrationUtils = {
 
         if (rootDir == SNAP_REAL_HOME) {
           targetPath = Services.env.get("SNAP_REAL_HOME");
+        } else if (rootDir === "Home" && Services.env.get("BB_ORIGINAL_HOME")) {
+          targetPath = Services.env.get("BB_ORIGINAL_HOME");
         } else {
           targetPath = Services.dirsvc.get(rootDir, Ci.nsIFile).path;
         }

browser/components/migration/content/migration-wizard.mjs

@@ -481,7 +481,10 @@ export class MigrationWizard extends HTMLElement {
     }
 
     let key = panelItem.getAttribute("key");
-    let resourceTypes = panelItem.resourceTypes;
+    const allowedTypes = ["BOOKMARKS"];
+    let resourceTypes = panelItem.resourceTypes.filter(t =>
+      allowedTypes.includes(t)
+    );
 
     for (let child of this.#resourceTypeList.querySelectorAll(
       "label[data-resource-type]"