Closed Bug 1537875 Opened 2 years ago Closed 1 year ago

favicon breaks certain website in private mode after first access


(Firefox :: Private Browsing, defect)

66 Branch
Not set





(Reporter: stacey_lane, Unassigned, NeedInfo)


User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:66.0) Gecko/20100101 Firefox/66.0

Steps to reproduce:

visiting: and

while in private browsing mode, eventually the site starts to return a blank page.

behaviour occurs in Firefox Quantum 66.0 (64-bit)

workaround is to close private browsing mode and open it again


about:config -> set = false

Actual results:

page works once or twice but then fails to load.
maybe there is a problem with caching in private mode.

in both cases the console indicates that favicon was not loaded properly

[Exception... "Component returned failure code: 0x80040111 (NS_ERROR_NOT_AVAILABLE) [nsIContentSniffer.getMIMETypeFromContent]" nsresult: "0x80040111 (NS_ERROR_NOT_AVAILABLE)" location: "JS frame :: resource:///modules/FaviconLoader.jsm :: onStopRequest :: line 230" data: no]
onStopRequest resource:///modules/FaviconLoader.jsm:230
InterpretGeneratorResume self-hosted:1255
next self-hosted:1210

I have ublock-origin loaded but I don't think that should be a problem.

Expected results:

page should display normally in private browsing mode without having to disable favicons

Hi reporter,

Thank you for taking the time to add this report. However, I was not able to reproduce it. I verified it using the latest release and Nightly builds on both Mac OS 10.14 and Windows 10. I tried accessing each site at least 5 times, because, as you mentioned in the actual results, they do work for the 1st or 2nd try, but for me, the sites loaded properly every time.

Could you please retest this using the latest FF release and latest Nightly build ( and report back the results? When doing this, please use a new clean Firefox profile, maybe even safe mode, to eliminate custom settings as a possible cause (

Component: Untriaged → Private Browsing
Flags: needinfo?(stacey_lane)

7 months without a response, closing as INCOMPLETE.

Closed: 1 year ago
Resolution: --- → INCOMPLETE
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