I'm trying to reproduce the issue with bubbles and my own GA data. I assume Sum(Pageviews) or sum(unique pageviews) is on Rows but what's on Colums? Date?? If you have two measures with one on Rows and one on Columns and Browser on the level of detail, then you should be able to use shapes with no problem.
Oh playing with this - maybe you are trying to get a packed bubble chart??? if so, that is sort of a special one. Would a scatter plot type view work?
Love to know what you came up with if you found your own solution. This is one of those rare occasions where I'd probably use a pie chart.
Thanks for your response and suggestions!
I was trying a packed bubble chart and wanted to have the entire bubble be the symbol for that browser. Had I not wanted to have it automated and updated daily or weekly, I would have made the packed bubble chart and then brought images into the dashboard to put on top of each bubble. Unfortunately, I wanted it to change with each update, and adjust accordingly.
I didn't like the look of it in a scatterplot. I ended up using a dual axis with the same data to create the visual. I made one version of the browser variable the bars and the duplicate browser variable was a shape. I then put the browser icons in My Tableau Repository, and I was able to use them. It ended up looking like this:
I wish we could use the shapes in the packed bubble chart, but for now, it doesn't seem like there is a way to do what I was trying to do. What I ended up with worked for what I needed to do, though.