I noticed that some (most? all?) words that were borrowed from English and end with -er in English can have either short or long vowel at the end:
browser - can be ブラウザ or ブラウザー
driver - can be ドライバ or ドライバー
computer - can be コンピュータ or コンピューター
Is one option preferred over another? There doesn't seem to be much consistency so is just a matter of personal choice? Dictionaries usually list both options so that doesn't offer much help.
Japanese 国語審議会 (National Language Council) recommends longer (with ー) forms since 1991. So foreign words in textbooks for elementary school students usually have trailing "ー".
http://www.mext.go.jp/b_menu/hakusho/nc/k19910628002/k19910628002.html
注3 英語の語末の‐er, ‐or, ‐arなどに当たるものは，原則としてア列の長音とし長音符号「ー」を用いて書き表す。ただし，慣用に応じて「ー」を省くことができる。 〔例〕 エレベーター ギター コンピューター マフラー
Japanese version of Microsoft Windows switched from "マイ コンピュータ" to "マイ コンピューター" as of Windows 7, according to this recommendation.
「コンピュータ」→「コンピューター」に MSが表記ルール変更 http://www.itmedia.co.jp/news/articles/0807/25/news090.html
However, as the article above explains, another standard from Japanese Industrial Standards (JIS規格の表記ガイドライン JIS Z 8301) has long said that "ー" should be omitted if the word is long enough, while convention always takes precedence.
http://kikakurui.com/z8/Z8301-2011-01.html
a)その言葉が 3 音以上の場合には，語尾に長音符号を付けない。
b)その言葉が 2 音以下の場合には，語尾に長音符号を付ける。
So your choice depends on the situation. Technologists and scientists tend to prefer shorter versions, while news media for general populations usually prefer longer ones.
(Here's NHK's policy: https://www.nhk.or.jp/bunken/summary/kotoba/gimon/159.html)
But anyway, in general, most Japanese don't care at all in their daily lives.
The "ー" at the end of the word is often (although not necessarily) omitted if it is a tech/computer related term. Even if "ー" is dropped, it comes back when it is read aloud. This applies to all three words in the question ("browser" is written "ブラウザ" and read "ブラウザー", for example), although the case for "driver" is special in that if it refers to a driver of a car it is written "ドライバー" and if it refers to a device driver it is written "ドライバ". To provide the example in the other way, since "curator" "キュレーター" isn't related to tech, the "ー" is never omitted.
More examples:
I remember seeing this rule explicitly written out somewhere in 「30日でできる！ OS自作入門」, and it matches my personal experience too. Not to discredit naruto, but I am pretty sure common Japanese people are not aware of any of the rules specified in that JIS spec ; p
From experience of sending a lot of business e-mails with customers in Japan, there doesn't seem to be a preferred way of writing it. It seems to be more depending on your age and where you learned it. Example:
Take the simulation with katakana. For me - and to many of my Japanese friends that I've asked - it should be written as シミュレーション, but in several of the mails I recieve some write it as シュミレーション. Older customers write the latter while younger write the former. This is also the case of other words such as excel-file which some writes エキセル and others エクセル.
Back to your question, this is the same situation. There is no general rule for when it should be either one. There are certainly other opinions about this but from my 10 years of experience, this is the conclusion I have drawn.
Observations seem to indicate the extended version is preferred. I tend to liken it to some British English accents where the final R is more of an extended A sound (e.g. "bar" sounds like "baa").
