1480219 - If TopSite screenshotting fails once for a url, that url will never get a screenshot (until the profile is cleared)

Status: NEW

(Firefox :: New Tab Page, defect, P3)

Description

[Adam Hillier :ahillier]

As a result of bug 1384094, if screenshot taking fails for a url, we don't ever try and take a new screenshot. However, screenshot taking may fail in a case where we would like the browser to try again, e.g. if caused by network failure.

This is most likely to happen on first run. 

STR:

1. Open Firefox with a fresh profile, immediately enter `xkcd.com` into the address bar and hit enter.

2. Once the page has fully loaded, quit Firefox. (So that the url exists in Places but a screenshot has not yet been taken.)

3. Disconnect from the internet and reopen Firefox. Observe that xkcd is the first TopSite, with no screenshot visible.

4. The screenshot process has been triggered, but will fail because of the disconnected network connection. Open the browser console and observe the failure message "getScreenshot(https://xkcd.com/) failed: Error: page-thumbnail:error" once the process times out (< 30 seconds).

5. Open the profile's thumbnails directory and observe that a zero byte .png has been saved. This is written as part of the fix to bug 1384094. This zero byte thumbnail blocks any future screenshot taking attempts, so the user is stuck with no screenshot for a topsite when one should be available.