@concretable
maybe there is something special with mac, I don't have experience with it...
but in windows drag and drop works fine, in Opera native manager and V7 Bookmarks

if you can't do it with drag and drop, you can select folders (in Opera native) clicking on check-circle in left corner and then right click and choose cut from context menu... after that, paste it where you want

I did tested first two extensions that you posted, in Opera stable standalone (usb) 58.0.3135.53
I had some problems at the beginning...
when I installed them, I couldn't see any of them on my extensions page and Opera kinda frozen...couldn't load any page

but after restart everything worked
I see previews on google search and notepad works (as far as I can tell)

btw. Opera is preventing extensions from injecting stuff on search results
you need to enable it first on opera://extensions

can you pls post the link to some of those extensions that do not work in Opera portable?
so that others can test it...

@k2103
you probably referring to sidebar extensions
they have icons on extensions bar (left vertical bar)

no,
extension icons on toolbar can only be on the right side of address field

you can use V7 History for that
either search for facebook in search field...
...or even better, simply click on facebook icon in sidebar list
this will act as a search for facebook in all titles and url's in history (much faster without typing in search field)

when you get results, there will probably be some items that are not from facebook domain
(like google results in red because there is a term facebook in title)
if you wish to filter only results from facebook domain, click on search term on top (in green)
this will give strictly results from favicon domain that you clicked

then click three dots on the top left corner and choose delete all

ps. this can be very slow process if there is a lot of url's (more than 100)...pls wait until extension is finished deleting

no... chromiums don't have that option
maybe there are extensions that can do that job

this is default font settings for win10 (latin)

you can find it in Opera settings under Appearance - > Customize fonts
and change to whatever you like

@lapsang yes

@blackbird71
well, Chrome allows adding other search engines as default
and there are other ways to prevent malicious code to add search engine as default, like strict user actions (eg. it must be performed by user)
I know that search engines are they way of income ...but still kinda sucks