Firefox suddenly won't start.

[Cinaed666]

After installing an addon, firefox fails to start.
The error in terminal is: GLib-CRITICAL **: g_slice_set_config: assertion `sys_page_size == 0' failed
I've tried to deleted local data folder and reinstalling it, but the problem persists?

[dentaku65]

Try to run FF ib safe mode:

firefox --safe-mode

[Doctor Colossus]

That error message is from a reported bug with no fix as of yet, and is probably unrelated. It seems like your problem was caused instead by the add-on, which you could uninstall from safe mode as suggested by dentaku65 or manually, by deleting the extension from your firefox profile directory.