Firefox "Start Loop Bug" with everything newer than SBIE 5.71.9

T

thomaz

New member
Hi, i have this problem:


As you can see i try to start firefox but it only crashes and restarts in a loop.
Sometimes when i then start firefox for one time outside sbie and after that retry it inside sbie, it works for some time, but then some time later it is again in this "Start Loop" state.

OS is fresh Win 11 Pro with May 2026 Updates.
I tried Firefox 140.11.0 ESR & Firefox 151.0.3 together with Sandboxie-Classic-x64-v5.72.6.exe

Firefox 140.11.0 ESR + 5.71.9 works perfekt.
Firefox 151.0.3 + 5.71.9 doesnt work (i think ff needs a newer sbie version).
 
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Thank you for your report and your video.

Does this also occur in a new/empty sandbox?

thomaz said:
OS is fresh Win 11 Pro with May 2026 Updates.
Click to expand...

What's your build-ID? (like 26200.8457)

Do you know if you have KB5089573 installed, which should be 2026-05 Preview and bump the build-ID to 26200.8524?

Firefox 151.0.3 with Sandboxie Plus 1.17.6 (which is the equivalent to 5.72.6) works on my Windows 11 Pro system, without it crashing, or without anything giving any warnings or errors.
 
I used Win11_25H2_English_x64_v2.iso and integrated the May 2026 KB5083769 Update into the .iso.
Then i installed it and ran it in this condition.
This Windows is locked down so it doesnt update itself.
Im not a friend of Windows Updates but it was a must because of this dangerous DNS-Client Vulnerability.
Before i ran old Win10 with old Sandboxie + latest Firefox ESR for years.

KB5089573 isnt installed and ver is 10.0.26200.8457.

Do i need KB5089573 to run Sandboxie without any Problems?

EDIT: i also have to correct myself, i now tested 151.0.3 with 5.71.9 and it works on the first view. no crash. sorry i thought it wouldnt run cause i read THIS here.
Also, atm im testing releases from 5.72.0+, i want to find out if 5.71.9 is really the last working version. I'm not 100% sure.
This was the last version i used for longer time without problems, but my first tests, now with 5.72.2 also look good.
The Installation of 5.72.3 the Start Loop Bug was there immediately, so i went back to 5.72.2.
This seems to be the absolute last working version for me.
BUT sometimes the bug appears a day later, mostly after a windows reboot, so i have to test some days :)

But 151.0.3 + 5.72.6 definitely also has this Start Loop Bug and Sandbox was completely empty (see config in video, it is set for auto delete).
 
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thomaz said:
Do i need KB5089573 to run Sandboxie without any Problems?
Click to expand...

No, I was just trying to check if that might be a contributing factor, since I don't have it installed. While I update regularly, I don't want to be the first in line, as so many updates caused issues.

Thank you for the additional information, maybe the developer can get a better understanding of what's happening.
 
It also doesnt matter if firefox profile is populated or empty (factory startup).
But firefox runs in portable mode by creating a profiles.ini.

%APPDATA%\Mozilla\Firefox\profiles.ini:
[InstallCENSOREDCENSORED]
Default=D:\_apps\firefox\profile

[Profile0]
Name=profile
IsRelative=0
Path=D:\_apps\firefox\profile
Default=1

[General]
StartWithLastProfile=1
Version=2
Click to expand...
 
Tried "Sandboxie-Classic-x64-v5.72.9.exe" today and the "Start Loop Problem" happend directly the 2nd time i tried to start ff 140.12.0esr.

v5.72.2 works like a charm since weeks now.
 
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