- deactivate all your other plugins, including our add-ons
Did that. The problem only occurs with slimstat activated.
- update to the latest version of Slimstat
I'm on 4.1.4.1.
- check your php error log for clues
With WP_DEBUG and WP_DEBUG_LOG enabled, I only get a notice relating to deprecated usage of load_plugin_textdomain by some plugins.
- check your PHP memory limit
There are no log entries about memory.
I suspect this is something related to the heuristic browser detector kicking in when a specific version of a browser is not listed in the browscap database.
The folks at bugzilla think the same (see bottom):
https://bugzilla.mozilla.org/show_bug.cgi?id=1174891