mozlz4-edit by Siarhei Kuzeyeu

Warning! You should not delete default search engines from a search.json.mozlz4 file if you edit the file. If you delete a default search engine then the Firefox will reset search engine list to a default state. But you can add new search engines.
Maybe there is another way to delete default search engines except Firefox Preferences menu but I don't know how.


How to
1. Find a search.json.mozlz4 file inside of your Mozilla Firefox profile folder.
2. Open the search.json.mozlz4 file with the mozlz4-edit extension.
3. Edit a search engine list.
4. Save the search.json.mozlz4 file in your Mozilla Firefox profile folder, replace the existed search.json.mozlz4 file by your new version.
5. Restart the Mozilla Firefox.


Note
There're .lz4 ( .jsonlz4, .jsonlz4-xxxx, .baklz4 etc) files inside of a Firefox's profile folder but actually they're mozlz4 files. You can try to open and edit these files.


Using without an installation
The extension can work as a simple local HTML page that you open in Firefox from your hard drive.
See the extension home page to know how to do that.


About permissions (The block for paranoids only!)
All these permissions are needed to let the extension works properly. Or at least it used to be like that. In future Mozilla may change permission system and add more options that let differentiate permissions more accurately.
If you have doubts you can use the extension without an installation as I described in the block above. In the case the extension will be executed in a Firefox sandbox as an usual local HTML page with limited permissions.