I love Firebug but Aaaarggggh.....!

[synystar]

I'm probably doing something wrong and there is probably a simple fix
for this... or perhaps it's a bug. I am using Firebug to modify CSS
on the fly for a site I am building on my local Apache server. It
works great for some time and then all of a sudden I am unable to make
any changes to the files. I click the Edit button but Firebug does
not allow me to edit and it will show a "circle-slash" symbol next to
lines that I hover the cursor over.

I created a clean profile with no other extensions other than Firebug
and the problem still occurs. I can't for the life of me figure out
what I'm doing wrong. Any ideas? I hope it's some stupid little
setting I'm overlooking. Thanks in advance.

[synystar]

... I should mention that the problem goes away if I close all Firefox
windows and restart, but not if I disable Firebug and re-enable. I'll
try to add more info here as the problem occurs unless someone knows
what's going already.

[smcoll]

does this happen after you refresh a page in the browser?