If you have a paid account with FoxyProxy, you can import your proxies here.
FoxyProxy can use Firefox Sync to synchronize settings across different installations of Firefox. But if you don't use Firefox Sync or want to share your settings with friends, FoxyProxy settings. Then use this page to import those settings. By default, the file is called _YYYY-MM-DD.json.
Firefox has completely changed the addon system since FoxyProxy 4.x and earlier. Older FoxyProxy versions used a pop-up window. It looked a little different on Windows, Mac, and Linux, but the essence was like the image below.
Unfortunately, due to Firefox 57+ limitations, we cannot read your FoxyProxy settings automatically. However, they are not lost. To import your old settings, please select the file foxyproxy.xml below. You can find it in the Firefox profile directory.
(click image for larger picture)