This bug is for crash report bp-e1f16774-561a-436b-b014-6ac150190424.

Top 8 frames of crashing thread:

0 xul.dll mozilla::dom::workerinternals::RuntimeService::CrashIfHanging dom/workers/RuntimeService.cpp:1785
1 xul.dll static void mozilla::`anonymous namespace'::RunWatchdog toolkit/components/terminator/nsTerminator.cpp:207
2 nss3.dll static void _PR_NativeRunThread nsprpub/pr/src/threads/combined/pruthr.c:397
3 nss3.dll unsigned int pr_root nsprpub/pr/src/md/windows/w95thred.c:137
4 ucrtbase.dll thread_start<unsigned int > 
5 kernel32.dll BaseThreadInitThunk 
6 mozglue.dll static void patched_BaseThreadInitThunk mozglue/build/WindowsDllBlocklist.cpp:712
7 ntdll.dll RtlUserThreadStart 

Steps to Reproduce

1. Launch Firefox with app.update.BITS.enabled pref to false.
2. Access the about:config page.
3. Set the app.update.BITS.enabled pref to true while Firefox is performing the download update process via nsIINcremental.
4. Restart Firefox.

Expected Result

• Firefox restarts successfully.

Actual Result

• Firefox crashes.

Regression Range

• I will get back with a regression range asap.

Additional Notes

• Please note that this issue is quite an intermittent one.
• We've used Netlimiter to simulate a poor network connection.

I'm suspicious that this hang may be unrelated to BITS. The crash report indicates that the problem is probably coming from IDBOpenDBRequest, which is part of indexedDB. Neither BITS nor any part of the updater uses indexedDB, so it seems unlikely that we are causing problems with it.

Additionally, there are examples of extremely similar looking crashes coming from before there was BITS code in the tree. Here is one.

To track this problem down, could you provide us with a bit more information?
Can you reproduce this problem?
If you disable automatic updates in about:preferences (Select "Check for updates but let you choose to install them"), can you reproduce the problem without updates ever being downloaded?

I tried reproducing this crash today using the steps from comment 0 but with no luck.. I also tested disabling the app.update.BITS.enabled while no updates are running and the browser restarted normally. I encountered this crash twice yesterday when changing app.update.BITS.enabled pref while download update was being performed. Changing this bug as worksforme because I can no longer reproduce the crash. I will keep an eye for this and will get back to you if I manage to reproduce this again.