Hi Daniel, we can't help implement your requests here in support, but I have a few comments based on my research: > search engine Search engine preferences have not been stored in the main preferences file (prefs.js) for many years, which could be why preferences Sync doesn't include them. If you are looking for a file to copy to a new profile, try '''search.json.mozlz4'''. I saw a request on file to Sync at least the default search engine if not all of them, but it doesn't have a high priority, so most likely someone with strong motivation will need to step forward and figure out how much to do and then code it up. (I imagine it will be a whole new category, alongside bookmarks, history, etc.) > tab cycling order What Ctrl+tab does -- recent order vs. left-to-right order -- should sync (assuming ''services.sync.prefs.sync.browser.ctrlTab.recentlyUsedOrder'' is true in about:config). However, as far as I can tell, tab Sync is limited to URLs. Did you need the date-time of the last access to sync? > overflow menu items I don't think any of the toolbar layout information is set up to sync. You could maybe transfer this using the following preference, at least for the built-in buttons and any matching extensions: browser.uiCustomization.state For example, you could update the value of the preference in the prefs.js file (while Firefox is closed). <blockquote> And the preferences from the extensions themselves should also be synced. </blockquote> Extension authors have the option to use either "local" storage or "sync" storage. However, sync storage is relatively small, so authors might be discouraged from using it. * https://developer.mozilla.org/docs/Mozilla/Add-ons/WebExtensions/API/storage/sync * https://developer.mozilla.org/docs/Mozilla/Add-ons/WebExtensions/API/storage/local You could ask the authors of extensions important to you whether sync storage could be added to their extensions.