The convert works well on sites with a few numbers that it identifies as a currency. I can easily overlook the smaller challenges there might be when it guess the currency wrong and the fiddling with the settings to make it work as you want it to.

Unfortunately some pages takes a lot of time to load or process data, as conversion can take some time to process pages with multiple amount of prices, even to the extend that Firefox itself suggest disabling it when it identifies that a page won't load.

Eventually i got around to do a performance analysis since loading a product page in a webshop made my pc fans go into turbo mode. It appears that this extension used 97% of the CPU time when loading a product page with 17 items.
While it probably adds additional nodes in the DOM and not just calculate a number, I don't fell like 97% CPU usage in 6 seconds is a good performance result.

Need to improve digits parser

Works, but slows the hell out of page loading.

Dramatically slows down the browser!

It works great and has a good interface, but on some pages, not sure if because of loading or otherwise, the extension starts to recursively convert values to the point where the tab crashes.

EDIT: Attempts to report the bug have resulted in no reply, and I cannot recommend this extension due to the inherent instability caused by it.