I like this add-on. It works very well. However, it sometimes warns me that Firefox is slow, especially in Gmail, and I recommend not using this add-on in Gmail. Fortunately, this add-on allows you to create a blacklist of sites, so you don't have to turn off the add-on feature every time you open Gmail.

Postscript (2023/06/23):
In this add-on, some image characters (?) are displayed as characters instead of images. For example, when you open https://translate.google.co.jp, you might see characters like "swap_horiz" and "star_border". The reference image can be found at the following URL: https://imgur.com/gallery/vsjC8eL.