To open the Performance tools:
- press Shift + F5
- select "Performance" from the Web Developer submenu in the Firefox Menu (or Tools menu if you display the menu bar or are on OS X)
- select "Performance" from Tools button, in the Toolbar, if you have one:
To start a new recording, press the stopwatch icon in the Recordings pane. To stop, press it again:
To save a profile, click the link labeled "Save" in the Recordings pane:
To load a profile, click "Import..." and choose the file:
To clear all loaded profiles, click "Clear".
If you do this, you'll lose any loaded profiles that you have not saved.
To control which markers are shown in the Waterfall, use the button in the toolbar:
To zoom into a slice of the recording, select that slice in the recording overview: