A good addon but a couple of auxiliary functions do not work:
1. Function for wrapping arguments in quotation marks.
2. The icon in the context menu does not change.

i have firefox 70, i just noticed right-click menu on the toolbar button is no longer there, to choose profile. and addon's entry is gone from firefox context menu too (i have always had it enabled for page and link contexts)

Excellent replacement for the Open With extension - although I agree with the previous reviewer that there is no need to enforce the selection of an icon (which doesn't seem to be used anyway unless the "Toolbar button" option is used), and that there needs to be an easy way to re-order the list of applications (the only way atm seems to be to remove and re-add each entry in the desired order, which necessitates picking the icon again every time).

It works, but all this circus with 'mandatory(?) icons' linked to site, which gives 16x16 black-white .ico in size of 350KB(!) - a bit annoying.

I don't like that's necessary to add a icon
You are forced to have all the stuff under the External Application Button. Not having that context menu would save us a click.
You can't rearrange the list of applications.

To open twitch streams using streamlink, in the Executable field you paste the path to streamlink.
C:\Program Files (x86)\Streamlink\bin\streamlink.exe
In the arguments field: [HREF] Best if you want to open the streams at best quality, [HREF] 480p if you want to open streams in 480 and so on..