Firebug has a minor bug in it’s css module:
What steps will reproduce the problem?
1. add combined css rule (#bd a, #bd a.myclass)
2. add css rule with specifity higher than the first rule of the combined selector and below specifity of the second rule of the combined selector (like #bd .myclass)
3. add e.g. different color definitions to the rules
What is the expected result? What do you see instead?
IS: firebug shows the css definitions of the single rule with higher specifity than the second selector of the combined rule > strikes the definition with the de facto higher specifity)

Firebug Bug : CSS Specifity Calculation
WANTED: strike through the definitions of the single rule with the lower specifity
Which version of Firebug? (more specific than latest please): 1.4.2
Which version of Firefox? 3.0.13
On what operating system? Windows XP Sp2
Testcase:
style.css
testcase-css-specifity
Bug # 2274 in Firebug Bugtracker
Bug # 2274