What's the meaning of Network activity groupings in Firebug Net tab

Question

What is the meaning of some splitter lines in the Net tab of the firebug:

In this picture line 1 and 2 seems to be in same group. And line 3 is grouped alone.

What's the meaning of these groupings?

Answer 1

In order to keep the X axis (time) in sensible extent, the waterfall graph breaks the time and starts displaying new requests that start later (in the page life) again from the beginning.

In other words, the request that starts after predefined period of time (1s by default) since the previous request finished, starts from 0 time of the graph again. This avoids endless extension of the X axis, which would make the graph less readable.

Every request that starts from beginning creates a new group. Groups are visually separated by a bit bolder horizontal line.

There is a preference extensions.firebug.netPhaseInterval [ms] that allows to set the gap after the time break should happen (set to 1000 by default). If set to 0, breaking doesn't happen at all (i.e. no grouping).

See also: http://www.softwareishard.com/blog/firebug/firebug-net-panel-timings/

Honza