It's not that difficult to change the maximum zoom number and it could benefit someone.
Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.
Can you elaborate on your expected use case and screen resolution? Currently unclear where >500% of zoom in browser would be of value at max res for most desktop/laptop/tablet systems (1920x1080).
500% zoom isn't nearly enough for viewing large SVG files in Firefox.
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