[FF] How to add/edit Gmail Category

X-notifier 3.5.18 and later
- this hidden feature option is obsolete -

The remaining available option for including the non-primary category count is to uncheck option 'Notify inbox only'. 

IF you want to remove the obsolete enableCategory preference from about:config:
1) [Right-click] the preference line and Reset
2) Restart Firefox  (this will remove your 'about:config' preference)

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X-notifier 3.3.4 to 3.5.17
(Right now, if you use old version of X-notifier,
Gmail won't work anymore,
Because their Gmail website updated.)

ALL INFORMATION BELOW, NO LONGER WORK!
I left this for history purpose.

Topic refers to:
extensions.xnotifier.accounts.[gmail#USERNAME].enableCategory : (0? 1? 2? see below)

1) Type 'about:config' in the location bar.
2) Look for gmail account with 'enabled' [Right-click] Copy Name
3) [Right-click] New => Integer
4) [Right-click] => [Paste] and replace 'enabled' with 'enableCategory'
5) [Click] OK
6) Enter Integer value ( 0  or  1  or   2   see below)

• 0 : disable
• 1 : show in folder view only
• 2 : get count from all enabled categories (tabs)

7) [Click] OK
8) Restart Firefox and ENJOY your new Gmail Category settings.

IF already setting, but you want to change value...
Just [Double-click] on value and input 0 or 1 or 2 [Click] OK

IF you want to remove it or "Forget it" (undo):
1) [Right-click] Reset
2) Restart Firefox  (this will remove your 'about:config' line)