There are two supporting features that are great for testers.
- Technical ability
- Domain knowledge
Technical ability is more along the lines of "I'm testing a game, and I know graphics libraries. I'm more likely to be able to spot rendering flaws." Domain knowledge "I'm an accountant, I will recognize a problem with accounting software faster than most people."
Both are excellent supporting features, but neither are required. The most important feature of a good tester is the ability to find bugs. These supporting features just give you a better understanding of the requirements, and it follows that understanding the requirements better will help you better find flaws in the program.
Ultimately, a good tester (or developer, or manager, or ANYTHING) is a quick learner and will be able to operate effectively even if you're unfamiliar. They're also more likely to seek knowledge on the topic. I don't know if there are accounting blogs (it doesn't sound too interesting, but I'm not an accountant) but perhaps taking half an hour or an hour to do some general research in accounting will help. I know there's a money Stack Exchange - perhaps you can ask, answer, or just read some questions there to get some better general knowledge about your given domain.
Any manager worth their salt is going to make allowances for someone who wants to actively become better at their job. After all, an hour a week is 2.5% of a 40 hour week. I would not find it difficult to imagine your productivity to go up by at least that with just a little bit of time.
Bottom line - if you can pick up domain knowledge, that's awesome, but don't beat yourself up over not having it.