[orca-list] Crashing orca 3.30.1 with by Braille paning in Firefox 60.3.0esr

[Raphaël POITEVIN <rpoitevin hypra fr>]

Dear team,

Orca 3.30.1 from Debian experimental, Firefox 60.3.0esr, brltty 5.4

Sorry if that bug has already been reported because that's so evident 
for a Braille reader.

1. Open any tab page
2. Pan Braille several time to right
3. Pan Braille several time to left.
Orca crashes.

debug log:
http://sprunge.us/w5Zt8n

Thanks for looking through that bug.

Regards,

Raphaël