I believe I have found a potential solution to the constantly crashing firefox in kubuntu issue.

I have just upgraded to KDE4.2 (that didn’t fix the problem, but is worth mentioning)

It uses Oxygen as it’s default theme.

I took a look at the GUI style being used in my QT Configuration (I’m not even sure why)

You can find the QT configuration app by searching your menu for “qt 4 settings”

I changed the GUI Style to oxygen to match the default theme for KDE 4.2 and then clicked the file menu and pressed save.

I then went to a known website that consistently caused crashing http://api.drupal.org/api/function/file_delete/6 and everything stayed running.

I suggest before you try the upgrade, navigate to the above test site, and scroll your mouse down.  If Firefox crashes, then try my solution.  If Firefox doesn’t crash, this solution may not work for yu.