Well it’s an alpha so there have to be a couple of these:

• “Highlight All” can break things. If you try to highlight all matches wierd things can happen to the document, and they might not go away when you unhighlight. Standard searching should be fine though.
• Crashes. This is implemented as a binary component which increases the risk of potentially crashing Firefox. I’m fairly confident that I’ve ironed out all the crashers there, but it’s possible I missed something, remember that this is an alpha release.
• Custom Firefox builds. Unfortunately because this extension uses a binary component, some custom builds of Firefox may not work well with it. Normally this should be spotted at startup and the regular expression option never shows itself, but in the worst case this could cause crashing. Please make sure you let me know if you are using a custom build of Firefox if you report a bug.

If you experience any other problems then please feel free to file a bug.