[Linux] Solved: Firefox fails to start

[IdOp]

For the past several weeks I've had a problem with Firefox crashing immediately at start-up on two of my Slackware Linux systems. In my investigations I found several similar problems reported elsewhere online, but either those reports went unanswered, or the answers they found didn't help me.

I've now found the cause of my Firefox problems, and just want to document the solution here, in case it helps someone else.

The Problems
The exact symptoms depend on which ff binary is used.

(a) Using the binary supplied by mozilla.org, a Crash Reporter window comes up giving the option to re-start or quit. Re-starting never works. The error message in the console is like this:

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ExceptionHandler::GenerateDump cloned child 1524
ExceptionHandler::SendContinueSignalToChild sent continue signal to child
ExceptionHandler::WaitForContinueSignal waiting for continue signal...

(b) If I use the Slackware-supplied binary of ff-ESR, a blank browser window comes up, and the console fills with error messages like:

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Crash Annotation GraphicsCriticalError: |[0][GFX1-]: Failed to lock new back buffer. (t=3.49651)

The Solution
After a lot of tests, frustration and dead ends, I found the problem (which was the result of "administrator error" ..., i.e., my bad!). It had to do ultimately with lack of user write permissions on /dev/shm . Normally, Slackware will mount a tmpfs on /dev/shm with the following line in /etc/fstab:

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tmpfs           /dev/shm         tmpfs       defaults         0   0

At one point I'd turned this off, forgotten about it, and much later ff stopped working (I don't use it regularly). As a result of this, the permissions on /dev/shm were those found on the root filesystem:

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drwxr-xr-x 2 root root          40 Dec  3 04:55 /dev/shm

which don't allow users to write to this space. Once the tmpfs is properly mounted again, the permissions look like this:

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drwxrwxrwt 2 root root          40 Dec  4 14:42 /dev/shm

Now users can write there and Firefox is happy.