Improve compatibility with Tab Kit 2

[fofajardo]

As reported on the forum.

• [x] Pale Moon
• [x] Basilisk

[fofajardo]

TabKit 2 has a difference in behavior between its versions for Pale Moon (0.13.3) & Basilisk (0.12.17):

Basilisk:

• Left edge tab bar - normal direction
• Right edge tab bar - reverse direction

Pale Moon:

• Left edge tab bar - reverse direction
• Right edge tab bar - normal direction

[fofajardo]

I've found out a few minutes ago that Tab Kit 2 (0.13.*) has incorrect labels:

Versions lower than 0.13 are unaffected (< 0.12.*)