To be fair, mozilla uses bugzilla to track everything, not just "bug" bugs. Each new feature in development has a bug, or multiple bugs. When code is refactored there is a bug for that, when somebody wants commit access there is a bug for that, when an employee needs a new laptop there is a bug for that, when a community organizer wants some money or gear for an event there is a bug for that, and so on... Other organizations use their bug/issue trackers in a similar manner.

Mozilla has passed the 1 million bugs _ever filed_ mark. Across all Mozilla products, for that matter.

Some possibly more useful statistics:

For the "Core" product (read: Gecko), there are as of right now 52k open bugs and 230k closed bugs.

For the "Firefox" product (desktop, not Firefox android), there are 21k open bugs and 128k closed bugs.

Note that these "bugs" include feature requests, so unless you think the number of requested features will decline over time....

> For most open source programs, it increases.

I know of at least one study that contradicts this claim:

"We found that with shorter release cycles, users do not experience significantly more post-release bugs and bugs are fixed faster, yet users experience these bugs earlier during software execution (the program crashes earlier)."

http://swat.polymtl.ca/~foutsekh/docs/Khomh-MSR-2012.pdf