I'd give it 5 stars but it doesn't allow you to use "ctrl+." as a keyboard shortcut, just "modifiers + alphanumerics", can you add this functionality? I bet it's a super small fix, thanks!

Edit: I did a bit of research, seems like you can add this behavior by adding the options for "," or "." with values "Comma", and "Period" (as an example if you add this two characters), those are the words Firefox understand for the "key combinations".

Edit 2: I was hoping that your extension was open source, what a joy to find that it was, I've been reading the source files and I think I've found a simple way for adding this functionality, I might be doing a pull request on these days :), hope it comes useful, thanks for your work!

Edit 3: I opened an issue and did a pull request for this change :)