The "switch to tab" feature is one of those improvements I believe didn't need to happen.
It has our best interests at heart but does a sloppy job of helping out.
What I sometimes do is load a dev page in one tab and keep it open. Then I make some changes and open a new tab to compare the changes.
The "switch to tab" feature makes it impossible for me to do this! A "feature" that prevents me from doing my job efficiently just has to go.
There is a bloody long discussion about this feature in the mozillazine forums but to be honest, it's too long and I didn't bother reading the whole thing.
If you want to disable this feature permanently, there are 2 add-ons that will do it for you. I'm unaware of how they work or how compatible they are with Firefox 5. See addons below in the sources section.
Personally, I didn't know but you can simply hold "Shift" while hovering your mouse over the "switch to tab" item.
It'll hide the switch-to-tab items and display the URLs as normal.