Cases and gig bags for left handed Firebird guitars
There are no hard cases made to fit left handed or right handed Firebird guitars other than proprietary brand cases which are made for their own brand models. Firebird bodies are too big to fit in shaped cases for the likes of Stratocaster, Les Paul, or PRS shape guitars.
There are no soft cases made to specifically fit left handed Firebird guitars.
There are a number of gig bags for Explorer and Firebird guitars and a few are ok for left-handed Firebirds too. See below:
THOMANN is a German musical instrument and musical accessories chain store that is all over Europe and the U.K. This gig bag is branded as a Thomann but is a bag sold under many other brand names and I am pretty sure they are all made at the same factory. I have compared all of these bags side by side and they are all identical. Thomann markets this bag as an Explorer and Firebird gig bag. It's a very good gig bag with 20mm padding. It is made for right handed guitars so a lefty guitar fits in face down instead of face up. I use this bag myself and have gigged for years with this gig bag without any problem. Unfortunately for us here in Australia by the time you do the currency conversion and add postage this gig bag is almost AU$200 per bag. I give the Thomann Firebird/Explorer gig bag a 8/10.
GB DELUXE is a bag I am very familiar with. I was using these for all my Gaskell Firebirds and Explorers until they stopped selling them in Australia. GB bags are heavy duty 600 Denier cordura nylon, made in India. The Firebird bag is slightly different than the GB Explorer gig bag (unlike THOMANN whose Explorer bag is also their Firebird bag.) There is a Premium version which is identical but has 30mm padding and costs more. As with all right handed Explorer gig bags the lefty has to be fitted in face down so the extra padding for the bridge and pickups isn't there. At US$ 69.95 it is fairly expensive and is only available from online music stores or eBay. I give the GB DELUXE (and PREMIUM) gig bag a 8/10.
Chromacast is a US company that sells musical accessories including instrument bags and cases. They have a good range of guitar bags. It appears they have discontinued it according to their website in 2023, but the CHROMACAST CC-EXTPB-BAG is (was?) a gig bag designed to fit "extreme" guitars of all kinds which includes Explorer, Flying V, Firebird, Kelly, etc. The good thing about this case is that it is roomy enough to be able to put a lefty Firebird in it without concern of it being the wrong way round / upside down which is a problem with all other Firebird/Explorer gig bags. My only concern with this bag is that it is a little flimsy and it would be better if it was more padded. But it could be ok judging by its specs. I give it 8/10 but the challenge will be finding one.
GATOR make some very good guitar bags. I have used many over the years and I like them. The GBE-EXTREME-1 is not one of their best in my opinion. This bag is a generic oversized bag meant to fit Explorers, Firebirds, Vs and other extreme shapes. It has 10mm padding and is essentially just a zip-up sleeve. You can lay your guitar any way in the bag so it doesn't have the issue of other gig bags as previously mentioned. However, because it is too thin I would not recommend this bag. You may as well wrap your guitar in a blanket. To be fair it is marketed as a budget gig bag and that is most definitely the case. At least you can put your guitar in it face up like it should go. I give it 6/10.
CHASE DIRECT is a UK online musical instrument and musical accessories store that sells cases for all musical instruments. Their gig bags are branded as "Chase." It looks like they only deliver within the U.K. I have not seen another one like this. It says it's an Explorer bag but that shape definitely will fit Firebirds. The bag has the usual problem with being a right handed bag but also has only 10mm padding. This would be a little risky to use for active musicians. I would not recommend this unless you really need to go somewhere with your guitar that isn't going to be an obstacle course, definitely not gigging. At GBP 29.99 at least it's not too expensive! Going by specs and looks this bag looks to be about a 5/10, lower only because of the thinner padding than others.