dirt fire trail and bar tab

1. What's a dirt fire trail? Is it an unpaved path used to prevent fire in the woods?

2. What's bar tab mentioned in the conversation I read from a novel called Sideways, by a writer called Rex Pickette?

"I've had a few glasses."
"A few glasses?" Jack laughed, slapping me on the back. "A few glasses, my bar tab!"

A fire trail is a road through the forest or bush, enabling firefighters to reach wildfires in remote areas.

A bar tab is the bill in a bar. Most bars charge you up front for a beverage, but if you're a good customer, or if it's a high end bar, they'll let you settle your bill on your way out the door. If you're an exceptionally good customer or a VIP, they'll let you run a tab indefinitely.

Thanks! But I don't understand what this guy meant by saying "my bar tab!". It seems to me he's being ironic. But what's he ironic about?

<A fire trail is a road through the forest or bush, enabling firefighters to reach wildfires in remote areas. >

Also these firetrails also act as a fire break preventing fires crossing into other areas of a forest or entering human habitant.

The bar 'tab' orginated from the old wooden pegs given to customers as prove they were owed by the bar.

Lazarakis, a "tab" is an amount you owe. To "run a tab" (especially in a bar or restaurant) is to be allowed to accumulate charges on your bill until the end of the night (or longer, if the bar owner really likes you), rather than having to pay for each individual drink or item as it is served to you.

<<Thanks! But I don't understand what this guy meant by saying "my bar tab!". It seems to me he's being ironic. But what's he ironic about?>>

He's not being ironic. Jack is kidding his friend that he (Jack) is the one who'll be paying for all those drinks that his friend has had.

"I've had a few glasses."
"A few glasses?" Jack laughed, slapping me on the back. "A few glasses, my bar tab!"

So Jack is saying that he bets the amount of his bar tab agains the veracity of the my statement that I have only had a few glasses -- he thinks the actual number of drinks I've consumed is much higher. You will see this construction in such common phrases as "She's 'just a friend', my ass!" -- related to "You bet your ass!" -- it's an expression of disbelief.

Ah! Okay. Uriel's explanation makes sense. I guess I read it differently. Scratch my earlier explanation.