I will add one information, which I don't know if it is related: If I go to
Preferences -> Connection Settings
and try to change the "Configure Proxy..." option, there is quite a delay in the clicking of the options.
Actually there is a delay in any of the selection bullets of the Preferences. It seems to be the same issue
and not related to downloads, file systems, etc, but to the selection form.
I confirm this problem in Mint 19.1 (Firefox 64).
I will add one information, which I don't know if it is related: If I go to
Preferences -> Connection Settings
and try to change the "Configure Proxy..." option, there is quite a delay in the clicking of the options.
Actually there is a delay in any of the selection bullets of the Preferences. It seems to be the same issue
and not related to downloads, file systems, etc, but to the selection form.