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About this Add-on
The plugin will add a status bar at the bottom right corner of Firefox and will display:
* TTFB: how long it took to see the first byte from remote server (from click to first byte received). This value gives a rough estimate on when the browser can start laying out the content.
* TTC: how long it took to display the page (from click to complete drawing of the page)
* Page size (number of bytes used to display the page): this value includes both bytes fetched from network and bytes fetched from the browser's cache.
Notes: that the above stat is only updated when a page is completely displayed (the progress bar is no longer displayed).
Some rule-of-thumbs on how to interpret/compare these metrics:
* For TTFB, shorter is better. Even for page that is large, a short TTFB (less then .5 sec) allows the browser opportunity to layout the page content as soon as possible. This can enhance the user's perception of responsiveness.
* TTC, obviously shorter is better. The current general agreement is that anything above the range of 7-10 seconds are perceived by user as slow.
* Page size, smaller is better. Most fast sites seem to max out around 75KB per page. Anything above 100KB tends to appear sluggish.
* Number of requests, smaller is better. Nowaday, with HTTP persitent widely supported, the cost of fetching another request no longer significant. But keep an eye for extreme cases (50+). This value tends to correlates well with the page size (large number of request -> large page size).
Keywords: timing, profile, optimize, stopwatch, measure page, http request
Regarding FF4, I've did a quick sanity check and did not find any error with FF4 so I updated the support version to 4.0.*
IMPORTANT: the "status-bar" (where lori displays the stats) is gone. The replacement, the add-on bar, is NOT enable by default. You will need to enable it. Use
View -> Toolbars -> Add-on Bar (check mark)
The View menu itself might be hidden by default, so you need to enable the View menu first. Sorry for all the hassle but these UI changes are not in my control.
Also, the number of request (req) looks wrong: always zero. I am not sure I will have time to look into that (will try). But from what I gather most people are interested only the timing anyway (the first two values) so probably is not a big lost.