It's possible to to get into a place where you can not remove it. When this happens, you need to use about:config to clear the breakpoint.

When does this happen:

1. source maps are used
2. the source changes
3. the debugger is opened/closed and debuggee is reloaded

I am still looking for simple STR, although i can reproduce it when i stress test the debugger.

Options:

1. update the code responsible for removing a bp so if the pending bp is not found, we remove the closest pending bp or all of the pending bps.
2. update the code responsible for syncing so that it never goes out of sync.