Which large percentage font are you referring to? Is it the percentage on the toolbar button badge or the percentage in the toolbar button popup? The percentage on the toolbar button badge can be removed. The percentage in the in the toolbar button popup needs to be a reasonable size to make it easily readable for visually impaired users.

Zoom Page WE will be unresponsive on pages where it cannot be used (e.g. the Mozilla Add-ons site). Are you finding it unresponsive on other pages? Please give an example link.