How can I get rid of strange files on my MacBook?

They are normal consequences of having used a Mozilla browser at one time, and having an older version of macOS or migrating that Mac's content from an older Mac, respectively.

You can drag them to the Trash if you wish, or just leave them be. They are harmless.

Maybe because I click a link in a e-mail that was a (spam) e-mail with a .php link that I clicked?

Nope. Although it's not a good idea to click links in an email message from an unknown or unexpected sender, that action alone (merely clicking a link in an email message) cannot install anything malicious on a Mac. It's what people do after clicking those links that can cause trouble, because they can load websites that attempt to convince you into providing personal or sensitive information. So don't do that. Read Recognize and avoid social engineering schemes including phishing messages, phony support calls, and other scams - Apple Support. It has a lot of good information and recommendations.

Almost certainly. Migrating content from an older Mac is the best way to set up its replacement, so you're doing it right. You can drag those files to the Trash if you want, or just leave them alone. When in doubt I prefer to leave them alone because they occupy such little space.

Yes. You should be able to locate all of the following (the forum truncated some of the names rather than wrapping them to the next line):

/System/Library/Templates/Data/System/Library/CoreServices/CoreTypes.bundle/Contents/Library/iLifeMediaBrowserTypes.bundle/Contents/MacOS/iLifeMediaBrowserTypes

/System/Library/Templates/Data/System/Library/CoreServices/CoreTypes.bundle/Contents/Library/iLifeMediaBrowserTypes.bundle

/System/Library/Templates/Data/Library/Application Support/iLifeMediaBrowser/Plug-Ins/iLMBPhotoBoothPlugin.ilmbplugin/Contents/MacOS/iLMBPhotoBoothPlugin

/System/Library/Templates/Data/Library/Application Support/iLifeMediaBrowser/Plug-Ins/iLMBPhotoBooth2Plugin.ilmbplugin/Contents/MacOS/iLMBPhotoBooth2Plugin

/System/Library/Templates/Data/Library/Application Support/iLifeMediaBrowser/Plug-Ins/iLMBPhotoBoothPlugin.ilmbplugin

/System/Library/Templates/Data/Library/Application Support/iLifeMediaBrowser/Plug-Ins/iLMBPhotoBooth2Plugin.ilmbplugin

(folder) /System/Library/Templates/Data/Library/Application Support/iLifeMediaBrowser

/System/Library/PrivateFrameworks/iLifeMediaBrowser.framework/iLifeMediaBrowser

(folder) /System/Library/PrivateFrameworks/iLifeMediaBrowser.framework

/System/Library/CoreServices/CoreTypes.bundle/Contents/Library/iLifeMediaBrowserTypes.bundle/Contents/MacOS/iLifeMediaBrowserTypes

/System/Library/CoreServices/CoreTypes.bundle/Contents/Library/iLifeMediaBrowserTypes.bundle

/Library/Application Support/iLifeMediaBrowser/Plug-Ins/iLMBPhotoBoothPlugin.ilmbplugin/Contents/MacOS/iLMBPhotoBoothPlugin

/Library/Application Support/iLifeMediaBrowser/Plug-Ins/iLMBPhotoBooth2Plugin.ilmbplugin/Contents/MacOS/iLMBPhotoBooth2Plugin

/Library/Application Support/iLifeMediaBrowser/Plug-Ins/iLMBPhotoBoothPlugin.ilmbplugin

/Library/Application Support/iLifeMediaBrowser/Plug-Ins/iLMBPhotoBooth2Plugin.ilmbplugin

(folder) /Library/Application Support/iLifeMediaBrowser

And these if you have Xcode installed:

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/PrivateFrameworks/iLifeMediaBrowser.framework/Versions/A/iLifeMediaBrowser.tbd

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/PrivateFrameworks/iLifeMediaBrowser.framework/iLifeMediaBrowser.tbd

(folder) /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/PrivateFrameworks/iLifeMediaBrowser.framework

The various iLifeMediaBrowser and iLMBPhotoBooth files are on every Mac. The OS installs them, including to the System folder which only Apple can touch. Ignore them.