This is how my family stores their respective Firefox profiles on the family computer: <nowiki>********** [General] StartWithLastProfile=1 [Profile0] Name=default IsRelative=0 Path=E:\<user>\Mozilla\ff\ff1 ********** The "E:\" partition is our user data partition. We keep Mozilla profiles there for two reasons: 1. Ease of backup. No need for YET ANOTHER special back-up rule. 2. All of the operating systems on the machine (we usually are running several via multi-boot) can use the same profiles, which hence do not become unsynchronized across the various operating systems. We do the same thing for Thunderbird: ********** [General] StartWithLastProfile=1 [Profile0] Name=Bellsouth IsRelative=0 Path=E:\<user>\Mozilla\tb\tb1 ********** So now we're evaluating Windows 10 Technical Preview... not on bare metal, but rather as virtualized by VMware Workstation 11.0, which treats partitions other than C: as mapped network drives. Hence, our profiles now look like: ********** [General] StartWithLastProfile=1 [Profile0] Name=default IsRelative=0 Path=\\vmware-host\Shared Folders\E\<user>\Mozilla\ff\ff1 ********** [General] StartWithLastProfile=1 [Profile0] Name=Bellsouth IsRelative=0 Path=\\vmware-host\Shared Folders\E\<user>\Mozilla\tb\tb1 ********** Note that VMware Workstation maps external partitions via "\\vmware-host\Shared Folders\<drive letter>". By the way, apps running on Windows 10 TP virtualized in general have no problems accessing our E: partition in this manner. Thunderbird is able to find and use the non-relative partitions without issue. However, Firefox fails to do so. After experimenting a bit, this is what appears to be happening: 1. Firefox appears in the Process List for less than one second and then disappears. 2. Firefox generates the error: "Firefox is already running, but is not responding. The old Firefox process must be closed to open a new window." 3. Click the "Close Firefox" button. 4. Firefox generates the error: "Your Firefox profile cannot be loaded. It may be missing or inaccessible." Well, that last error is infamous... but we learned long ago how to find/fix missing profiles. This is something else altogether. Is the problem simply that Firefox cannot have profiles on mapped network drives... but Thunderbird can? Or is there some other issue lurking here? Thanks in advance for your assistance. Best regards, ...milo47 </nowiki> P.S. I'm writing this on Firefox on Windows 7 / SP1 / Pro / x64 on bare metal... not under Windows 10... so the Troubleshooting Information is misleading. Obviously, I cannot run Firefox yet on Windows 10! But, for what it's worth, I don't use many plug-ins, and the version of Firefox on Windows 10 is absolutely up-to-date.