Hello,,

It's not as convenient as bookmarks... If you have a backup program/service backing up your Firefox profile folder, your search engine plugins are in there. More specifically you can find them as follows:

Open your current Firefox settings (AKA Firefox profile) folder using either

   "3-bar" menu button > "?" button > Troubleshooting Information
   (menu bar) Help > Troubleshooting Information
   type or paste about:support in the address bar and press Enter 

In the first table on the page, click the "Show Folder" button. This should launch a new window listing various files and folders in Windows Explorer.

Find the folder searchplugins and copy its contents to a safe place every so often.

Many versions ago Firefox migrated the search engine plugin data to a compressed file named search.json.mozlz4 stored in your active profile folder. See: Profiles - Where Firefox stores your bookmarks, passwords and other user data.

This file probably is most useful as a whole, but if you need to read the file contents, I have a decompression script you can run in Firefox's Browser Console, or a web page with a similar tool on my site:

• Decompression script: https://gist.github.com/jscher2000/4403507e33df0918289619edb83f8193
• Webapp: https://www.jeffersonscher.com/ffu/searchjson.html

Once Firefox has extracted the data from the OpenSearch .xml file and stored it in that file, I don't think it's easy to reconstruct the original, but it would be an interesting project. (These interesting projects keep piling up!)

See also this extension.

• mozlz4-edit https://addons.mozilla.org/firefox/addon/mozlz4-edit/

"How do i sync or backup my search engine"?

With Sync, user installed search engines are are limited to search engines which are installed from and available at the Addons.Mozilla.Org website {AMO}. Mycroft Project add-ons and all other search engines obtained elsewhere won't be synchronized by Sync. The reason is that Sync doesn't sync each users own Add-on/extensions, but rather Sync installs them afresh from the AMO server when a new Profile is connected to Sync or when the user uses Sync to 'populate' a newly purchased device. And Search Engines are now 'packaged' as Add-on/ extensions, thus the limitations carry forward into the Sync process. PIA, for sure, but just the way that Sync was made to work when the option to 'sync' add-on/ extensions was added to Sync 5 or 6 years ago. (Sync was added to Firefox 4.0, which was released on March, 22 2011, as a new built-in feature.)

So as jscher2000 mentioned, using the search.json.mozlz4 file as a "backup" is your best bet. I have done that repeatedly when creating a new Profile in Firefox and when I set up a new PC with Firefox. Never had the need to do anymore with regards to a "web app", and haven't yet tried the extension/Add-on that corel linked.