Hi I tried with ui vision in my firefox 68.4.0esr (64 bit) with ui vision 5.3.10 and this bug does not occur I advise you to ask the admin to access the virtual machine and try the bug in the admin virtual machine in order to allow him to have an error log and correct.
Some bug are related to the versions of firefox, ask for access to the testing virtual machine so you can replicate the bug and the admin can correct it.
I tried all firefox version to choice the best version for ui vision, with some version i have more bugs.
Read here how you can try to reproduce the bugs in virtual machine, i use RDP to test ui vision and inform admin of bugs.