I've fired my bulb up only a few times so far, but today I realized some yellow stuff forming inside of it (see image).



Is this normal?

yep, little glass bits in there is alright as well, cracks are bad, but your bulb will burn out fast if you have air getting in, but yeah theres somewhre on the guide that mentions how this is 100% normal, chemical reaction stuffs

its basically a pool of sulfer or solidified sulfer now

alright cool, thanks a lot. always better to be sure when it comes to such stuff.