Are you still facing this issue? I just tried using an add-on, and it worked fine for me.
Can you specify which one you tried? Also, I'd suggest you try once after clearing the cache/cookies of the browser to see if that makes any difference.
This shouldn't be happening! Would you be able to share a screen recording for us to review and investigate it? Also, can you try working on an incognito/private browser once and let us know about the observations?