There are two things I would love to be done:
1) Ability to set background color as yours is too dark and black images are poorly visible
2) Extension works only with SVG files that are browsed online, when I open saved SVG it's not affected by extension. I collect some SVG's for the work and need to browse them. Using Firefox for that purpose will be great.

Otherwise it's a useful extension indeed. I don't understand why all browsers center bitmap images, but doesn't center SVGs.