Get add-on id of extensions in Firefox

Open about:memory. Click "measure" in Show memory reports. In the Main Process section, scroll down to Other Measurements. There you will find the installed (active) extensions with their names and their ids displayed as baseURL=moz-extension://[random-ids].

This method works for both Firefox and Firefox for Android. Note that only enabled extensions are shown.

I tried the other two and they both worked but I really had to search to find which extension was which

I found that using about:debugging was very clear as to which extension was which I̶ ̶a̶l̶s̶o̶ ̶h̶a̶d̶ ̶t̶o̶ ̶c̶l̶i̶c̶k̶ ̶̶T̶h̶i̶s̶ ̶F̶i̶r̶e̶f̶o̶x̶̶ ̶a̶f̶t̶e̶r̶ ̶t̶h̶e̶ ̶p̶a̶g̶e̶ ̶l̶o̶a̶d̶e̶d̶

Just go to about:debugging#/runtime/this-firefoxand it will give you the following

• Extension Picture next to Extension Name
• Extension ID
• Internal UUID
• Manifest URL