[Req] Add it as a sidepanel on Firefox

[Fred-Vatin]

Hi,

At least, as an option, it would be great to use in the sidepanel instead of the current floating dialog covering the page.

[FallenMax]

@Fremea Hi, porting latest version to FireFox is be tracked with #31.

Side panel seem like a good idea, it will be great if we can completely avoid content covering. But I guess to make it work nicely across all sort of websites and different layouts is not easy. I will take a look and evaluate.