The rounded corners of RadEditor consist of table cells that are empty. In order to prevent improper rendering of these cells we have added a . When the default font size of the Firefox is changes the size of the &nbps; is changed as well which leads to the observed appearance problem.
Unfortunately, this behavior cannot be controlled by CSS, i.e. 1px is 1px no matter what the default font size of the browser is. Another example - if you use the zoom function of Firefox and IE the size of the elements will change, however there size in pixels will remain the same.
The toolbar problem is very rarely reported because the Minimum Font Size setting in Firefox is not popular.
the Telerik team
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