Silverlight Plugin Unable to do Height Percentage in Firefox

I recently published a video on resizing Silverlight controls.  I just observed an odd behavior in the Firefox browser when setting the height of the plugin to any percentage (10%, 50%, 100%).  I can set the width to 100%, as the screenshot below indicates:

silverlight in firefox browser with width at 100%

Notice the height is set to 100, not 100%.  Now, if I change the height to 100%, this is what happens:

setting height to 100% causes silverlight control to disappear in silverlight

By setting the height to a percentage (of any number) in Firefox, my silverlight control disappears.  If I set the height to a percentage in other browsers - the control behaves as it should.  Anyone know why height percentage does not work in Firefox?


  • This isn't a Silverlight-specific issue. It has to do with the way Firefox handles HTML OBJECT layout. To work around this, set the CSS display attribute for your OBJECT to block (display: block).

  • Thats because the object element's ancestors do not have a height set. In this case, you have an object inside a div, inside a div, inside the body. Nothing I see sets a height, so, therefor, the relative height you have set for the object has nothing to be relative to.

  • Joe Chung,

    Setting the object css display attribute did not work. Thanks for the feedback anyway.

  • Will Green,

    Your advice did put me on track to the solution. I added the following to my javascript to get height percentage to work in Firefox:

    // change element height to window height in firefox
    if (window.innerHeight)
    { = window.innerHeight + "px";

  • Setting the object's CSS display to block works if you don't set the DOCTYPE as shown in your screenshots. If you set the DOCTYPE, it won't work.

  • Scratch my last reply. It appears that the Silverlight script overrides default HTML OBJECT processing, DTD or not.

  • Pete Blois,

    Unfortunately that is not true. Joe Chung made that clear in one of his comments. Silverlight script overrides what would typically work.

    I did find a solution that does work, and it is in a previous comment.

  • any resolution to this issue? I am having the same problems.

  • style="position:fixed;left:0;top:0;height:100%;width:100%"

    may have ie6 issues though.

  • Yeeahhooo!
    Thanks Will, it work!

  • An even easier option was to add the following style to the SilverlightContainer DIV tag:


    The Silverlight object then picks up the height (and width) that is defined in the Silverlight object, whether it is percentage or pixel based.

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