New WPMU 2.7.1 install with only one blog. I installed the wpmu-dixi theme and played around with the configuration. Uploaded a new header image, changed the sidebar widgets a little, and changed the copy on the About page. Then I tried to add my first Post. As soon as I press the "Add Media" button Firefox crashes. I have never seen Firefox crash like that before.
I tried exactly the same thing with Google Chrome and it worked properly - I wrote my Post and inserted an image with no problems.
Then I switched back to Firefox and it crashed again exactly the same way.
I have another WPMU 2.7.1 system with different themes (no wpmu-dixi) and I don't have any problems using Firefox.
My Firefox is 3.0.10 running on Windows XP Pro.
Here's the content of wp-content/mu-plugins/:
additional_tags.php forums-framework.php admin-footer-text.php login-image.php admin-message.php readme.txt all-in-one-seo-pack remember-me-checked.php all_in_one_seo_pack.php remove-permalinks-menu-item.php avatar-comments.php remove-wp-dashboard-widgets.php avatar-posts.php simple-sitemaps.php avatars.php widget-avatar.php custom-content-dashboard-widget.php
Will try this later tonight on a different system. Very odd.