@Jabby - the other thing you can do with the Sigil 0.5.90x releases is turn on the auto tokenising/escaping of ctrl+F text. What this feature does is if you are in Regex mode (where I tend to stay) and select some text and hit ctrl+F it will automatically make it "safe" to use in a regular expression. If you have line feeds/multiple spaces they get converted to \s+. And importantly for this particular question if your selected text contains characters that have special meanings in regular expression like asterisks, periods, brackets etc then they will get automatically escaped with a preceding \ for you.
And yet another way of doing this if you don't have that option on is to right-click on the Find dropdown and choose "Tokenise Selection", which will do a very similar thing (except it also adds converting numbers into \d+).
With the tokenising/escaping option turned on I find it extremely rare that I ever have a need to switch back to "Normal" mode for F&R.
As to where you enable it, that is a bit complicated by the fact that it has moved for the upcoming 0.5.907 release. If you are using 0.5.905/6 you will find it under Search->Regex Options. As of 0.5.907 all those options have moved to become checkboxes on the F&R dialog itself which are much more accessible and visible.